METHOD AND APPARATUS FOR DATA COMMUNICATION

Abstract: A data communication method includes the steps of: sending a communication procedure signal prior to data communication; sending a data signal; and sending a stop signal for stopping an echo suppressor function on a communication network; wherein the stop signal is sent prior to the data signal in such a way that a time interval during which no signal is generated does not occur, after the stop signal is sent, until the data signal is sent. A data communication apparatus includes: a communication unit for sending and receiving a data signal; a discrimination unit for discriminating if the apparatus is a calling station; and a control unit for controlling to change a communication controlling mode based on the output from the discrimination unit.

Description: The present invention relates to a data communication method and a data communication apparatus for sending and receiving data such as character code data, image data or the like via a communication network, particularly suitable for application to data transmission via an international communication network. Of the data communication apparatus, facsimile apparatus for example are known for sending and receiving image information. In case where a conventional facsimile apparatus calls a receiving station in an automatic sending mode, it is possible for the facsimile apparatus to perform necessary procedures by confirming by itself that the apparatus operates as a calling station. However, for the case that a calling is made by a telephone set prior to sending image information with the facsimile apparatus, a conventional facsimile apparatus is not constructed in such a way that it can confirm or detect by itself that it operates as a calling station. Alternatively, in case where a conventional facsimile apparatus is previously set at an automatic receiving mode, it is possible for the facsimile apparatus to perform necessary procedures by confirming by itself that the apparatus operates as a receiving station. However, for the case that the facsimile apparatus is set at a manual receiving mode, a conventional facsimile apparatus is not constructed in such a way that it can confirm to detect by itself that it operates as a receiving station. In this case, only an audible ringing of the telephone is generated. By transmitting an echo suppressor function termination tone to a receiving station prior to commencing necessary data communication over an international communication network, it is possible to send a control signal from a called station to a calling station during data transmission from the calling station to the called station (i.e., so-called full duplex operation). However, on the contrary, a full duplex operation cannot be achieved even if a control signal is sent from a calling station to a called station during data transmission from the called station to the calling station, although an echo suppressor function termination tone was sent prior to commencing an international communication. Therefore, if a "continuous error retransmission" is intended in the latter case (during data transmission from a called station to a calling station), the image information sending station cannot detect a control signal (e.g., a NACK signal which is sent when a reception error occurs) so that data communication becomes impossible. This is a serious disadvantage associated with a conventional facsimile apparatus. The "continuous error retransmission" here mentioned means an error retransmission system in a full duplex operation. More in detail, according to the system, when an error is detected at a receiving station during transmission of image information from a sending station, the receiving station sends a NACK signal to the sending station to suspend transmission of image information. Thereafter, the image information is retransmitted starting from for example the address frame line where the error was generated. In case of the facsimile apparatus, for example, the echo suppressor function is stopped upon sending a called station identification signal (CED) to use the telephone network in a full duplex mode. However, even if the echo suppressor function is once stopped, this stoppage is released if signals are not being sent for a period longer than a predetermined time interval. For instance, if it takes a long time for the operator at a sending station to depress a sending start button after hearing a CED signal, response signals NSS/TSI/DCS cannot be sent from the sending station in response to first, initial identification signals NSF/CSI/DIS sent from the receiving station. Consequently, the receiving station must send the initial identification signals once again. However, since signals are not being sent for a relatively long period between the first and second initial identification signals, the stoppage of the echo suppressor function is made released. In addition, if a receiving station cannot receive signals of DCS group or page interruption signals such as EOP, MPS, EOM or the like, the stoppage of the echo suppressor function is made released also in this case. Releasing the stoppage of the echo suppressor function makes it impossible to communicate in a full duplex mode. Accordingly, the continuous error retransmission using the network in a full duplex mode becomes also impossible. Moreover, this prior art involves a data communication method for use on a communication network which method comprises the steps of sending a communication procedure signal prior to data communication and sending a data signal, wherein the correct transmission of said data signal is controlled by means of a continuous error retransmission. Prior to a sending of control signals said continuous error retransmission is stopped by the suppression of an echo suppressor function. Moreover, this echo suppressor function can be stopped by a stop instruction which is automatically released after a time interval during which no signal is generated. Thus, there exists a distinguishing difference between the communication of control signals which is done in a half duplex mode and the communication of data which is done in a full duplex mode. The use of said stop signal according to the prior art is also implemented in an known apparatus wherein the communication of control signals in said half duplex mode is effected also between different pages to be sent and between training procedures which are used before starting data communication. However, said time interval for releasing said stop instruction is normally too short for an operator because it takes a long time for him to depress a sending start button after hearing a called station identification signal. Due to this fact response signals cannot be sent from the sending station in response to first initial identification signals because in the meantime the stoppage of the echo suppressor function is already released. The same problem of releasing the echo suppressing function too early also occurs during communication of data which exist of a plurality of pages. Nevertheless, releasing the stoppage of the echo suppressor function makes it impossible to communicate in a full duplex mode which is used during communication of data signals. Therefore, it is an object of the invention to provide a communication method and a communication apparatus without the afore mentioned problems and disadvantages. According to the invention, a stop signal including said stop instruction for stopping said echo suppressor function is sent prior to the communication of said data signal so that said time interval does not occur. Thus, by means of always switching off said echo suppressor function before sending data signals a full duplex mode which is preferably used for data communication is established. That is, the control communication is done in half duplex mode and, in contrast thereto, the data communication is done in full duplex mode which is achieved by preventing a release of said stoppage of said echo suppressor function which release would make it impossible to communicate in said full duplex mode. Document EP 0 116 650 A1 describes a facsimile transmission control system of the G3 group wherein, in order to shorten the transmission times, parts of the control sequences are transmitted at a high data-transmission rate or wherein control sequences are partly renounced, respectively. Control signals are sent before the actual data transmission starts. Document DE 26 53 965 A1 describes an echo suppressor function intended to filter out the line echos occurring in a full duplex operation. In particular, reflection echos caused by mismatching are to be avoided. On the other hand, in the case of the subject matter of the present application a CRC sum is normally retransmitted during the real data transmission and, when an error occurs, the defective transmission block is resent. This echo function is stopped when control signals are transmitted and/or the echo suppressor function enables a transmission of control signals during the running data transmission. In contrast thereto, in document DE 26 53 965 A1 the stop instruction of the echo suppressor function is released after a predetermined time interval during which no signal is generated. Moreover, the echo suppression is continuously in operation and serves a purpose so as to filter out the line echos occurring in full duplex operation. Fig. 1 schematically shows the output timings of signals at the sending and receiving stations according to a first embodiment of a data communication system according to the present invention; Fig. 2 is a circuit block diagram showing an embodiment of a facsimile transmitter of the first embodiment; Fig. 3 is a control flow chart for the control circuit shown in Fig. 2; Fig. 4 is a block diagram showing a second embodiment of a facsimile apparatus to which the present invention is applied; Fig. 5 is a flow chart showing the control procedure of the control circuit 36 of Fig. 4; Fig. 6 is a block diagram showing a third embodiment of a facsimile apparatus to which the present invention is applied; and Figs. 7A and 7B are flow charts showing the control procedure of the control circuit 240 of Fig. 6. A first embodiment of the present invention will now be described with reference to the accompanying drawings. Fig. 1 shows the output timings of output signals at the sending and receiving stations in the embodiment of a facsimile communication system according to the present invention. First, upon reception of a calling signal CI from the sending station, the receiving station outputs a called station discrimination signal CED. Thereafter, the receiving station sends an initial discrimination signal NSF indicative of a non-standard function to notify the sending station as to whether a continuous error retransmission function is provided at the receiving station. This is done for example by setting one of the bits, for example, the 50th bit in facsimile information field NSF FIF at 1 for the presence of the error retransmission function and at 0 for the absence of that function. The receiving station also sends a called station identification binary signal CSI and a digital identification signal DIS. On the side of the sending station, it is judged whether the operator has selected the error retransmission function and whether the receiving station has that function. If the operator has selected the error retransmission function and if the receiving station has this function, then the 50th bit in FIF of a non-standard facsimile setting signal NSS is set at 1 to send it to the receiving station. The sending station also sends a sending station identification signal TSI and a digital command signal DCS. The receiving station can judge based on the signal NSS whether the error retransmission function can be used. Upon reception of a reception preparation confirmation signal CFR from the receiving station, the sending station sends, if the error retransmission function is to be used, a tonal signal of 2100 Hz for 1 sec as an echo suppressor function termination tone EST. Thereafter, with no signals being sent for a period shorter than 100 ms or less, or without sending any signals, the sending station sends a training signal and a message (image) signal. Consequently, it is possible to use the network in a full duplex mode during transmission of message. Thus, even if a part of image signals cannot be received at the receiving station during message transmission, the continuous error retransmission system can operate to retransmit the error portion. After completion of a one-page transmission, if there is a next page, the signal NSS is again sent. Also in this case, it is noted that a signal EST prior to sending a training signal and a following message signal is sent to the receiving station. After the end of the transmission of all the pages, the sending station sends a network open signal DCN to complete the communication. An embodiment of a facsimile transmitter performing the procedures of Fig. 1 is shown in Fig. 2 in the form of a block diagram. Referring now to Fig. 2, a network control unit NCU 2 controls to connect a telephone station to a telephone network, connect a data communication path to the telephone network for using it as data communication, or hold a loop. A signal line 2a represents a telephone line. The NCU 2 is inputted with a signal from a signal line 28a and connects the telephone line to the telephone station, i.e., connects the signal line 2a to a signal line 2b, on condition that a signal level "0" is inputted from the signal line 28a. On the contrary if a signal level "0" is inputted from the signal line 28a, the NCU 2 connects the telephone line to the facsimile station, i.e., connects the signal line 2a to a signal line 2c. In an ordinary state, the telephone line is maintained connected to the telephone station. Reference numeral 4 represents a telephone set. A hybrid circuit 6 performs separation between sending signals and receiving signals. In particular, sending signals on a signal line 18a are send to the telephone network via the signal line 2c and the NCU 2. Receiving signals are delivered onto a signal line 6a via the NCU 2 and the signal line 2c. A reading circuit 8 sequentially reads from an original to be transmitted one-line image signals in the main scan direction and generates a signal train made of binary signals of white and black. The reading circuit 8 is constructed of an image sensor such as a charge-coupled device and an optical system. The signal train binarized as of white and black is outputted to a signal line 8a. An encoder 10 is inputted with binarized data from the signal line 8a and encodes it. The encoder 10 has a memory whose capacity is sufficient for retransmission purpose. The encoder 10 encodes the binarized data so as to be suitable for an ordinary transmission in case that a signal level "0" is inputted from a signal line 28d, while on the other hand it encodes the binarized data so as to be suitable for a continuous error retransmission in case that a signal level "1" is inputted from the signal line 28d. During the continuous error retransmission mode, the following control is performed. When a signal line 28b takes a signal level "1", the image transmission is interrupted. If the signal line 28b becomes signal level "0", information at the retransmission start line outputted onto a signal line 28c is inputted to the encoder circuit 10 which in turn retransmits information starting from the start line. Data subjected to MH (Modified Huffman) encoding or MR (Modified Read) encoding is outputted onto a signal line 10a. A modulator 12 performs modulation in conformity with known CCITT Recommendation V27 ter (differential phase modulation) or V29 (orthogonal modulation). The modulator 12 is inputted with a signal from the signal line 10a and modulates it to output modulated data onto a signal line 12a. A modulator 14 performs modulation in conformity with known CCITT V21, which is inputted with a procedure signal from a signal line 28e and modulates it to output modulated data onto a signal line 14a. Information on the 50th bit in NSS FIT is outputted onto a signal line 28f. An echo suppressor function termination tone generating circuit or EST generating circuit 16 generates a signal EST when a pulse appears on a signal line 28g. In this embodiment, as a signal EST, a signal of 2100 Hz continues to be sent for one second. The EST generating circuit 16 generates a pulse onto a signal line 16b when delivery of a signal ESP is completed. An adder 18 is inputted with signals from signal lines 12a, 14b and 16a and outputs the added result onto the signal line 18a. A demodulator 20 performs demodulation in conformity with known CCITT Recommendation V21, which is inputted with a signal from the signal line 6a and V21-demodulates it to output a demodulated signal onto a signal line 20b. The demodulator 20 also outputs information on the 50th bit in NSS FIF onto a signal line 20a. The receiving station outputs a signal NACK onto the signal line 6a when the station detects a reception error. A NACK signal detecting circuit 22 generates a pulse onto a signal line 22A when signal NACK is detected. A retransmission start line detecting circuit 24 detects the retransmission start line number to be sent following a signal NACK, and outputs the line number onto a signal line 24a. A continuous error retransmission mode selection detecting circuit 26 detects if the operator has selected the retransmission mode. The circuit 26 outputs a signal level "0" onto a signal line 26a in case that the operator has not selected the continuous error retransmission mode. On the contrary, if the operator has selected the retransmission mode, the circuit 26 outputs a signal level "1" onto the signal line 26a. A control circuit 28 performs the following controls. In case where the operator at the sending station has not selected the continuous error retransmission mode as yet or the receiving station has no continuous error retransmission function, an ordinary transmission is carried out. In this case, a signal EST is not sent immediately before the image signal is sent. In case where the receiving station has the continuous error retransmission function and the operator at the sending station has selected the retransmission mode, the transmission is carried out under the continuous error retransmission mode. In this case, a signal EST is sent immediately before the image signal is sent. When a retransmission is intended, the signal EST is again sent immediately before the image signal is sent. Thus, a full duplex operation becomes possible even over an international communication network. The control circuit 28 is constructed of such as a CPU, ROM, RAM and the like. In Fig. 3, a flow chart for the control procedure of the control circuit 28 of Fig. 2 is shown. The content of this flow chart is stored in the ROM of the control circuit 28. Referring now to Fig. 3, the telephone network is connected to the telephone station at step S50 to send a calling signal CI. If the start button is depressed after detection of a signal CED at step S52, then the telephone network is connected to the hybrid circuit at step S54. At step S56 a signal NSF from the receiving station is received to judge at step S58 whether the receiving station has the continuous error retransmission function. If present, it is checked at step S60 if the operator has selected the retransmission function. If not present at anyone of steps S58 and S60, then a normal mode is selected at step S61 to output a signal level "0" onto the signal lines 28b, 28d and 28f. On the other hand, if present at both steps S58 and S60, then the continuous error retransmission mode is selected to output a signal level "0" onto the signal lines 28b, 28d and 28f. Thus, a signal NSS, i.e., "1" at the 50th bit in FIF is sent at the pre-procedure at step S64. Upon detection of a signal CFR (Confirmation to Receive) at the pre-procedure at step S64, an echo suppressor function termination tone signal EST is sent at step S66 and thereafter, with no signals being sent for a period shorter than 100 ms or less or without any signals being sent, a training signal and a message (image) signal are sent at steps S68 and S70. Consequently, the communication network is always used in a full duplex mode during message transmission in the continuous error retransmission mode. If a signal NACK is received from the receiving station during message transmission, a retransmission start line number signal following the signal NACK is detected at step S74. After preparation of the retransmission at step S76, step S66 resumes to sequentially send a signal EST, training and message signals. Upon detection of the end of a one-page message at step S78, it is judged at step S80 whether a next page is present or not. If present, step S58 resumes to repeat the above operations. If not present, a signal DCN is sent to complete the operations. In case where an ordinary mode is selected at step S61, then a signal NSS, i.e., "0" at the 50th bit in FIF is sent at the pre-procedure at step S82 and thereafter, the ordinary mode proceeds without sending a signal EST. As described in the foregoing, the facsimile apparatus of this embodiment always sends, in a continuous error retransmission mode, a signal EST immediately before image signal data is transmitted. Therefore, even if signals are not being send for a period longer than 100 ms or more during the procedure, the communication network can always be used in a full duplex mode during practical data communication. This is very advantageous for international or remote communication wherein generally a long time is required in transmitting information and the network quality is not always good. In the above embodiment, although a signal EST is sent immediately before the training signal which is sent prior to the image signal, it is also possible to send a signal EST before the image signal which includes signals not being sent for a period longer than 100 ms or more. As seen from the foregoing description of the first embodiment, even if signals are not being sent during a communication procedure, the communication network can always be used in a full duplex mode during practical data communication, reliably performing a continuous error retransmission operation. It is advantageous particularly for international or remote communication where absence of signals to be sent during the procedure is likely to occur. Next, a second embodiment of the present invention will be described. First, a brief description of the operation will be given wherein the receiving station is provided with the continuous error retransmission function, the operator at the sending station has selected the retransmission mode, and the start button for international communication has been depressed. In such a state, the sending station confirms by itself as to whether the sending station is a calling station or a called station, with the aid of calling station identification means to be described later in detail. In case that the sending station is a calling station, transmission of image information is performed in the continuous error retransmission mode. Declaration for transmission in the continuous error retransmission mode is effected by a signal NSS. Alternatively, in case that the sending station is a called station, low speed transmission of image information is initiated. Declaration for this low speed transmission is effected by a signal DCS. If the operator at the sending station has not selected the continuous error retransmission mode, a normal transmission of image information is performed. It is not concerned at all in this case whether the receiving station is provided with the continuous error retransmission function and whether the operator at the sending station has depressed the start button for international communication. In case that although the operator at the sending station has selected the continuous error retransmission mode, the receiving station is not provided with the continuous error retransmission function, low speed transmission of image information is initiated. It is not concerned at all in this case whether the operator at the sending station has depressed the start button for international communication. In case that the receiving station is provided with the continuous error retransmission function and that the operator at the sending station has selected the retransmission mode but not depressed the start button for international communication, transmission in the continuous error retransmission mode is performed. The construction and operation of a second embodiment of the facsimile apparatus will be described in detail in the following. Referring now to Fig. 4, a network control unit NCU 102 controls to connect a telephone station to a telephone network, connect a data communication path to the telephone network for using it as data communication, or hold a loop. A signal line 102a represents a telephone line. The NCU 102 is inputted with a signal from a signal line 136a and connects the telephone line to the telephone station, i.e., connects the signal line 102a to a signal line 102b, on condition that a signal level "0" is inputted from the signal line 136a. On the contrary if a signal level "0" is inputted from the signal line 136a, the NCU 102 connects the telephone line to the facsimile station, i.e., connects the signal line 102a to a signal line 102c. In an ordinary state, the telephone line is maintained connected to the telephone station. Reference numeral 104 represents a telephone set. A hybrid circuit 106 performs separation between sending signals and receiving signals. In particular, sending signals on a signal line 118a are send to the telephone network via the signal line 102c and the NCU 102. Receiving signals are delivered onto a signal line 106a via the NCU 102 and the signal line 102c. A reading circuit 108 sequentially reads from an original to be transmitted one-line image signals in the main scan direction and generates a signal train made of binary signals of white and black. The reading circuit 108 is constructed of an image sensor such as a charge-coupled device (CCD) and an optical system. The signal train binarized as of white and black is outputted to a signal line 108a. An encoder 110 is inputted with binarized data from the signal line 108a and encodes it. The encoder 110 has a memory whose capacity is sufficient for retransmission purpose. The encoder 110 encodes the binarized data so as to be suitable for ordinary transmission in case that a signal level "0" is inputted from a signal line 136d, while on the other hand it encodes the binarized data so as to be suitable for continuous error retransmission in case that a signal level "1" is inputted from the signal line 136d. During the continuous error retransmission mode, the following control is performed. When a signal line 136b takes a signal level "1", the image transmission is interrupted. If the signal line 136b becomes signal level "0", information at the retransmission start line outputted onto a signal line 136c is inputted to the encoder circuit 110 which in turn retransmits information starting from the start line. Data subjected to MH (Modified Huffman) encoding, MR (Modified Read) encoding or error retransmission encoding is outputted onto a signal line 110a. A modulator 112 performs modulation in conformity with known CCITT Recommendation V27 ter (differential phase modulation) or V28 (orthogonal modualtion). The modulator 112 is inputted with a signal from the signal line 110a and modulates it to output modulated data onto a signal line 112a. If a signal line 136e is signal level "0", high speed transmission of modulated data is performed for example at 9600 bit/sec of V29 . Alternatively if the signal line 136e is signal level "1", low speed transmission of modulated data is performed for example at 4800 bit/sec of V27 ter. A modulator 114 performs modulation in conformity with known CCITT Recommendation V21, which is inputted with a procedure signal from a signal line 136f and modulates it to output modulated data onto a signal line 114a. An echo suppressor function termination tone generating circuit or EST generating circuit 116 generates a signal EST onto a signal line 116a when a pulse appears on a signal line 136g. In this embodiment, as a signal EST, a signal of 2100 Hz continuous to be sent for one second. The EST generating circuit 116 generates a tone delivery end pulse onto a signal line 116b when delivery of a signal ESP is completed. An adder 118 is inputted with signals from signal lines 112a, 114b and 116a and outputs the added result onto the signal line 118a. A demodulator 120 performs demodulation in conformity with known CCITT Recommendation V21, which is inputted with a signal from the signal line 106a and V21-demodulates it to output a demodulated signal onto a signal line 120a. The receiving station outputs a signal NACK onto the signal line 106a when the station detects a reception error. A NACK signal detecting circuit 122 generates a pulse onto a signal line 122a when the signal NACK is detected. A retransmission start line detecting circuit 124 detects the retransmission start line number to be sent following a signal NACK, and outputs the line number onto a signal line 124a. A selection signal sending circuit 126 is inputted with dial number information outputted on a signal line 136i when a pulse is generated onto a signal line 136h, to thereby send a selection signal onto a signal line 126a. The dial number is given by an operation section 130 to be described later. Input methods for the dial number from the operation section 130 are such as one-touch dialing method, shortened dialing method, dialing method using numerical keys or the like. As the selection signal, a DC impulse or push-button dial signal may be used. A selection signal detection circuit 128 is inputted with a signal from the signal line 102b to detect if a selection signal is inputted from the telephone station. As the selection signal, a DC impulse signal or push-button dial signal may be used. When a selection signal is sent from the telephone station, the selection signal detecting circuit 128 outputs a signal of level "1" onto a signal line 128a. When the network becomes open, the selection signal detecting circuit 128 outputs a signal of level "0" onto the signal line 128a. When a selection signal is sent from the telephone station or when a selection signal is sent from the selection signal sending circuit 126, and the facsimile apparatus is connected to the network, then it is confirmed that the facsimile apparatus is at a calling station. The operation section 130 includes such as a start key, mode setting key, numerical keys, alphabetical keys, one-touch keys, and the like. The information signal inputted from the operation section 130 is outputted onto a signal line 130a. A continuous error retransmission selection detecting circuit 132 detects if the operator has selected the retransmission mode. The circuit 132 outputs a signal level "0" onto a signal line 132a in case that the operator does not select as yet the continuous error retransmission mode. On the contrary, if the operator selects the retransmission mode, the circuit 132 outputs a signal level "1" onto the signal line 132a. An international communication button depression detecting circuit 134 detects if the operator has depressed the button. The circuit 134 outputs a signal of the level "0" onto a signal line 134a in case that the button is not depressed as yet. On the contrary, if the button is depressed by the operator, the circuit 134 outputs a signal of level "1" onto the signal line 134a. A control circuit 136 performs the following controls. The description is made assuming that a calling is received and a connection for facsimile transmission has been established. In case that the receiving station is provided with the continuous error retransmission function, and that the operator at the sending station has selected the retransmission mode and has depressed the start button for international communication, the sending station discriminates whether it is a calling station or a called station. If it is a calling station, a transmission in the continuous error retransmission mode is performed. Alternatively, if it is a called station, a low speed transmission of image information is initiated. If the operator at the sending station has not selected the continuous error retransmission mode, a normal transmission of image information is performed. It is not concerned at all in this case whether the receiving station is provided with the continuous error retransmission function and whether the operator at the sending station has depressed the start button for international communication. In case that although the operator at the sending station has selected the continuous error retransmission mode, the receiving station is not provided with the continuous error retransmission function, a low speed transmission of image information is initiated. It is not concerned at all in this case whether the operator at the sending station has depressed the start button for international communication. In case that the receiving station is provided with the continuous error retransmission function and that the operator at the sending station has selected the retransmission mode but not depressed the start button for international communication, a transmission in the continuous error retransmission mode is performed. Declaration for transmission of image information in the continuous error retransmission mode is effected by a signal NSS, while declaration for the low speed transmission of image information is effected by a signal DCS. The control circuit 136 is constructed of such as a CPU, ROM, RAM and the like. In Fig. 5, a flow chart for the control procedure of the control circuit 136 of Fig. 4 is shown. The content of this flow chart is stored in the ROM of the control circuit 136. Referring now to Fig. 5, the telephone network is connected to the telephone station at step S150. That is, a signal of level "0" is outputted onto the signal line 136a. From step S152 to step S164, if it is judged as a sending station at the auto/manual network connection, "1" is set at a flag HASSIN. If it is judged as a receiving station, "0" is set at the flag HASSIN. That is, the actuation requirements of the facsimile apparatus are checked at steps S154, S156 and S158 by setting at step S152 "0" at the flag HASSIN. Setting at step S164 "1" at the flag HASSIN is conducted in case where a calling is made from the operation unit (the control circuit 136 is inputted with a dial number from the signal line 130a and a selection signal is sent from the selection signal sending circuit 126), or in case where the start button has been depressed after a calling is made from the telephone station. Setting of the flag HASSIN is not performed at the other actuation requirements, i.e., when an automatic reception is effected or when the start button is depressed after a manual reception is effected. The characteristic feature of this embodiment resides in that even at the manual mode operation (i.e., the start button is depressed after the network is connected using the telephone station), the facsimile apparatus concerned discriminates whether it is a sending station or a receiving station. This discrimination is conducted by the selection signal detecting circuit 128 (corresponding to the judgement at step S160). That is, at step S160 the control circuit 136 is inputted with a signal from the signal line 128a and judges, in case the signal is at level "1" , that a calling from the telephone station was effected. After actuation based on one of the various actuation requirements, the telephone network is connected to the facsimile apparatus (steps S158, S159, S162). Control for this connection is conducted by outputting a signal of signal level "1" onto the signal line 136a. At step S166 it is judged whether the continuous error retransmission mode has been selected, i.e., whether the signal line 132a is at signal level "1". If the continuous error retransmission mode has been selected, i.e., if the signal line 132a is signal level "1", then step S174 follows. If the continuous error retransmission mode is not selected as yet, i.e. ,if the signal line 132a is signal level "0", then step S168 follows. Step S168 is a pre-procedure. At this step, a normal transmission mode is declared. Step S170 is a normal image transmission step at which a signal of a signal level "0" is outputted to the signal lines 136d and 136e. Step S172 is an after-procedure. At step S174 it is judged whether the receiving station is provided with the continuous error retransmission function, which is judged based on a procedure signal (signal NSF) outputted on the signal line 120a. In case that the reception station is provided with the retransmission function, step S176 follows. If not, step S188 follows. At step S176 it is judged whether the international communication button has been depressed, i.e., if signal line 134a is signal level "1". In case the button has been depressed, i.e.in case the signal line 134a is signal level "1", then step S178 follows. Alternatively if the international communication button is not depressed as yet, i.e., if the signal line 134a is signal level "0", then step S180 follows. At step S178 it is judged whether the facsimile apparatus concerned is a calling station, i.e., if the flag HASSIN is "1". In case of the calling station, i.e., in case the flag HASSIN is "1", then step S180 follows. If not, i.e., if the flag HASSIN is "0", then step S188 follows. At step S180 transmission in the continuous error retransmission mode is selected. In particular, signal levels "1" and "0" are outputted to the signal lines 136d and 136e, respectively. Step S182 is a pre-procedure, at which image information transmission in the continuous error retransmission mode is declared by signal NSS. At step S184 image information transmission is performed in the continuous error retransmission mode. While image information transmission is performed using an international communication network, an echo suppressor function termination tone EST is sent from the EST generating circuit 116 immediately before an image signal is sent. A signal NACK is also detected by the NACK signal detecting circuit 122. The retransmission start line number to be sent following the signal NACK is detected by the retransmission start line detecting circuit 124. Next, if an error retransmission is intended, a signal representative of the retransmission start line number is outputted onto the signal line 136c to inform the encoder 110 of the retransmission start line number. The encoder 110 starts the image information retransmission from the retransmission start line number. Step S186 is an after-procedure. At step S188 low speed transmission of image information is selected. In particular, signal levels "0" and "1" are outputted onto the signal lines 136d and 136e, respectively. Step 190 is a pre-procedure, at which low speed transmission of image information is declared by signal DCS. At step S192 low speed transmission of image information is performed. Step S194 is an after-procedure. In the above embodiment, if the error retransmission mode is selected for communication over an international communication network, low speed transmission of image information is controlled to be performed from the called station to the calling station. However, besides such control method an error retransmission in a half duplex (so-called stop-and-wait error retransmission mode) may be applied. Furthermore, in the above embodiment although depression of the international communication button is detected to judge whether communication is initiated, it is also possible to automatically judge initiation of an international communication by receiving initial identification signals NSF/CSI/DIS. As seen from the foregoing description of the second embodiment of the present invention, prior to sending and receiving data, the facsimile apparatus concerned can discriminate by itself whether it is a calling station or not. Therefore, it is possible to properly perform the succeeding transmission control procedure. For instance, if the error retransmission mode is selected for an international communication, data transmission from the calling station to the called station is performed in the error retransmission mode, while data transmission from the called station to the calling station is performed at low speed. Therefore, a disabled status in communication as conventional can be avoided even during data transmission from the called station to the calling station. Next, a third embodiment of the present invention will be described. First, a brief description of the operation will be given wherein the receiving station is provided with the continuous error retransmission function, the operator at the sending station has selected the retransmission mode, and the start button for international communication has been depressed. In such a state, the sending station confirms by itself as to whether the sending station is a calling station or a called station, with the aid of calling station identification means and storing means for storing information whether the facsimile apparatus concerned is a called station, to be described later in detail. In case that the sending station is a calling station, transmission of image information is performed in the continuous error retransmission mode. Declaration for transmission in the continuous error retransmission mode is effected by a signal NSS. Alternatively, in case that the sending station is a called station, low speed transmission of image information is initiated. Declaration for this low speed transmission is effected by a signal DCS. If the operator at the sending station has not selected the continuous error retransmission mode, a normal transmission of image information is performed. It is not concerned at all in this case whether the receiving station is provided with the continuous error retransmission function and whether the operator at the sending station has depressed the start button for international communication. In case that although the operator at the sending station has selected the continuous error retransmission mode, the receiving station is not provided with the continuous error retransmission function, low speed transmission of image information is initiated. It is not concerned at all in this case whether the operator at the sending station has depressed the start button for international communication. In case that the receiving station is provided with the continuous error retransmission function and that the operator at the sending station has selected the retransmission mode but not depressed the start button for international communication, transmission in the continuous error retransmission mode is performed. The construction and operation of a third embodiment of the facsimile apparatus will be described in detail in the following. Referring now to Fig. 6, a network control unit NCU 202 controls to connect a telephone station to a telephone network, connect a data communication path to the telephone network for using it as data communication, or hold a loop. A signal line 202a represents a telephone line. The NCU 202 is inputted with a signal from a signal line 240a and connects the telephone line to the telephone station, i.e., connects the signal line 202a to a signal line 202b, on condition that a signal level "0" is inputted from the signal line 240a. On the contrary, if a signal level "0" is inputted from the signal line 240a, the NCU 202 connects the telephone line to the facsimile station, i.e., connects the signal line 202a to a signal line 202c. In an ordinary state, the telephone line is maintained connected to the telephone station. Reference numeral 204 represents a telephone set. A hybrid circuit 206 performs separation between sending signals and receiving signals. In particular, sending signals on a signal line 218a are sent to the telephone network via the signal line 202c and the NCU 202. Receiving signals are delivered onto a signal line 206a via the NCU 202 and the signal line 202c. A reading circuit 208 sequentially reads from an original to be transmitted one-line image signals in the main scan direction and generates a signal train made of binary signals of white and black. The reading circuit 208 is constructed of an image sensor such as a charge-coupled device (CCD) and an optical system. The signal train binarized as of white and black is outputted to a signal line 208a. An encoder 210 is inputted with binarized data from the signal line 208a and encodes it. The encoder 210 has a memory whose capacity is sufficient for retransmission purpose. The encoder 210 encodes the binarized data so as to be suitable for ordinary transmission in case that a signal level "0" is inputted from a signal line 240d, while on the other hand it encodes the binarized data so as to be suitable for continuous error retransmission in case that a signal level "1" is inputted from the signal line 240d. During the continuous error retransmission mode, the following control is performed. When a signal line 240b takes a signal level "1", the image transmission is interrupted. If the signal line 240b becomes signal level "0", information at the retransmission start line outputted onto a signal line 240c is inputted to the encoder circuit 210 which in turn retransmits information starting from the start line. Data subjected to MH (Modified Huffman) encoding, MR (Modified Read) encoding or error retransmission encoding is outputted onto a signal line 210a. A modulator 212 performs modulation in conformity with known CCITT Recommendation V27 ter (differential phase modulation) or V29 (orthogonal modulation). The modulator 212 is inputted with a signal from the signal line 210a and modulates it to output modulated data onto a signal line 212a. If a signal line 240e is signal level "0", high speed transmission of modulated data is performed for example at 9600 bit/sec of V29. Alternatively if the signal line 240e is signal level "1", low speed transmission of modulated data is performed for example at 4800 bit/sec of V27 ter. A modulator 214 performs modulation in conformity with known CCITT Recommendation V21, which is inputted with a procedure signal from a signal line 240f and modulates it to output modulated data onto a signal line 214a. An echo suppressor function termination tone generating circuit or EST generating circuit 216 generates a signal EST onto a signal line 216a when a pulse appears on a signal line 240g. In this embodiment, as a signal EST, a signal of 2100 Hz continues to be sent for one second. The EST generating circuit 216 generates a tone delivery end pulse onto a signal line 216b when delivery of a signal ESP is completed. An adder 218 is inputted with signals from the signal lines 212a, 214a and 216a and outputs the added result onto the signal line 218a. A demodulator 220 performs demodulation in conformity with known CCITT Recommendation V21, which is inputted with a signal from the signal line 206a and V21-demodulates it to output a demodulated signal onto a signal line 220a. A NACK signal detecting circuit 222 is inputted with a signal from the signal line 206a and generates a pulse onto a signal line 222a when it detects a signal NACK sent from the receiving station. A retransmission start line detecting circuit 224 detects the retransmission start line number to be sent following a signal NACK, and outputs the line number onto a signal line 224a. A reception detecting circuit 226 is inputted with a signal from the signal line 202b. When it detects a calling signal of 16 Hz, the reception detecting circuit 226 outputs a signal of signal level "1". An auto/manual reception setting circuit 228 can be set as desired by an operation section 234 to be described later. If a manual reception mode is set, the circuit 228 outputs a signal of a signal level "0" onto a signal line 228a. If an auto reception mode is set, it outputs a signal of a signal level "1" onto the signal line 228a. An AND circuit 230 is inputted with signals from signal lines 226a and 228a and outputs its result onto a signal line 230a. In contrast, according to the conventional facsimile apparatus, the signal on the signal line 230a is inputted to a control circuit as a reception signal. In other words, a reception is confirmed on condition that an auto reception mode is set and a calling signal of 16 Hz is received. However, according to the facsimile apparatus of this embodiment, the signal on the signal line 226a is directly inputted to the control circuit as a reception signal. Therefore, even if a manual reception mode is set, the facsimile apparatus can detect by itself a reception. In this case, an audible ringing of the telephone is generated with the telephone network connected to the signal line 202b. A storage circuit 232 functions to store information whether the facsimile apparatus is a called station. In particular, to write the information on whether the facsimile apparatus is a called station, data (a signal of level "1" for a called station, and a signal of level "0" for a calling station) is outputted onto a signal line 240h and thereafter a write pulse is generated onto a signal line 240j. Contrary, to read the information on whether the facsimile apparatus is a called station, the data is read via the signal line 240h after generating a read pulse onto a signal line 240i. The operation section 234 includes such as a start key, mode setting key, numerical keys, alphabetical keys, one-touch keys, and the like. The information signal inputted from the operation section 234 is outputted onto a signal line 234a. A continuous error retransmission selection detecting circuit 236 detects whether the operator has selected the retransmission mode. The circuit 236 outputs a signal level "0" onto a signal line 236a in case that the operator does not select as yet the continuous error retransmission mode. On the contrary, if the operator selects the retransmission mode, the circuit 236 outputs signal level "1" onto the signal line 236a. An international communication button depression detecting circuit 238 detects whether the operator has depressed the button. The circuit 238 outputs a signal of level "0" onto a signal line 238a in case that the button is not yet depressed. On the contrary, if the button is depressed by the operator, the circuit 238 outputs a signal of level "1" onto the signal line 238a. A control circuit 240 performs the following controls. The description is made assuming that a calling is received and a connection for facsimile transmission has been established. First, if a calling is established, it is discriminated if the facsimile apparatus concerned is a called station. The discrimination information is stored in the storage circuit 232 for storing information on whether the apparatus is a called station. Such a procedure is carried out in both automatic and manual reception modes. In case that the receiving station is provided with the continuous error retransmission function, and that the operator at the sending station has selected the retransmission mode and has depressed the start button for international communication, the sending station discriminates whether it is a calling station or a called station. If it is a calling station, a transmission in the continuous error retransmission mode is performed. Alternatively, if it is a called station, a low speed transmission of image information is initiated. If the operator at the sending station has not selected the continuous error retransmission mode, a normal transmission of image information is performed. It is not concerned at all in this case whether the receiving station is provided with the continuous error retransmission function and whether the operator at the sending station has depressed the start button for international communication. In case that although the operator at the sending station has selected the continuous error retransmission mode, the receiving station is not provided with the continuous error retransmission function, a low speed transmission of image information is initiated. It is not concerned at all in this case whether the operator at the sending station has depressed the start button for international communication. In case that the receiving station is provided with the continuous error retransmission function and that the operator at the sending station has selected the retransmission mode but not depressed the start button for international communication, a transmission in the continuous error retransmission mode is performed. Declaration for the transmission of image information in the continuous error retransmission mode is effected by a signal NSS, while declaration for the low speed transmission of image information is effected by a signal DCS. The control circuit 240 is constructed of such as a CPU, ROM, RAM and the like. In Figs. 7A and 7B, flow charts for the control procedure of the control circuit 240 of Fig. 6 is shown. The content of these flow charts is stored in the ROM of the control circuit 240. Referring now to Fig. 7A, the telephone network is connected to the telephone station at step S250. That is, a signal of level "0" is outputted onto the signal line 240a. From step S252 to step S270, if it is judged as a sending station at the auto/manual network connection, a signal of level "0" (indicative of non-called station) is written in the storage circuit 232 for storing information on whether the facsimile apparatus is a called station. Alternatively, if the facsimile apparatus is a called station, a signal of level "1" (indicative of called station) is written in the storage circuit 232 for storing information on whether the facsimile apparatus is a called station. First, at step S252 a signal of level "0" (indicative of non-called station) is written in the storage circuit 232 for storing information on whether the facsimile apparatus is a called station. In case that an auto reception mode is set (which is decided by the input signal from signal line 228a) and when a reception is detected (when an auto reception is detected), information that the facsimile apparatus is a called station is stored (a signal of level "1" is written in the storage circuit 232 for storing information on whether the apparatus is a called station) to thereafter advance to step S272. When a reception is detected (which is decided by the input signal from signal line 226a), "1" is set at a flag X which is set with "0" at the time of initialization and on-hook state. A manual operation starts when the start button is depressed. After depression of the start button, the content of the flag X is checked. If the content of the flag X is "1", the facsimile apparatus is judged as a receiving station and such information is stored (a signal of level "1" is written in the storage circuit 232 for storing information on whether the apparatus is a called station) to thereafter advance to step S272. If the content of the flag X is "0" under depression of the start button, it is judged that the apparatus is a sending station. Also in case an automatic sending is performed by the operation unit 234, the apparatus is judged as a sending station to thereafter advance to step S272. At step S272 the telephone network is connected to the facsimile station, i.e., a signal of signal level "1" is outputted onto the signal line 240a. At step S274 shown in Fig. 7B, it is judged whether the continuous error retransmission mode has been selected, i.e., if the signal line 236a is at a signal level "1". If the continuous error retransmission mode has been selected, i.e., if the signal line 236a is the signal level "1", then step S282 follows. If the continuous error retransmission mode is not yet selected, i.e., if the signal line 236a is a signal level "0", then step S276 follows. Step S276 is a pre-procedure. At this step, a normal transmission mode is declared by the signal NSS/DCS. Step S278 is a normal image transmission step at which a signal of signal level "0" is outputted to the signal lines 240d and 240e. Step S280 is an after-procedure. At step S282 it is judged whether the reception station is provided with the continuous error retransmission function, which is judged based on a procedure signal (signal NSF) outputted on the signal line 220a. In case the reception station is provided with the retransmission function, then step S292 follows. If not, step S284 follows. At step S284, a low speed transmission of image information is selected. In particular, signal levels "0" and "1" are outputted onto the signal lines 240d and 240e, respectively. Step S286 is a pre-procedure, at which the low speed transmission of image information is declared by a signal DCS. At step S288 the low speed transmission of image information is performed. Step S290 is an after-procedure. At step S292, it is judged whether the international communication button has been depressed, i.e., if the signal line 238a is a signal level "1". In case the international communication button has been depressed, i.e., the signal line 238a is the signal level "1", then step S294 follows. Alternatively, if the international communication button is not still depressed, i.e. , the signal line 238a is a signal level "0", then step S296 follows. At step S294, it is judged whether the facsimile apparatus concerned is a called station, based on the input data from the storage circuit 232 for storing information on whether the apparatus is a called station. In case of the calling station, then step S284 follows. If not, then step S296 follows. At step S296 transmission in the continuous error retransmission mode is selected. In particular, signal levels "1" and "0" are outputted to the signal lines 240d and 240e, respectively. Step S298 is a pre-procedure, at which image information transmission in the continuous error retransmission mode is declared by a signal NSS. At step S300 image information transmission is performed in the continuous error retransmission mode. While image information transmission is performed using an international communication network, an echo suppressor function termination tone EST is sent from the EST generating circuit 216 immediately before an image signal is sent. A signal NACK is also detected by the NACK signal detecting circuit 222. The retransmission start line number to be sent following the signal NACK is detected by the retransmission start line detecting circuit 224. Next, if an error retransmission is intended, a signal representative of the retransmission start line number is outputted onto the signal line 240c to inform the encoder 210 of the retransmission start line number. The encoder 210 starts the image information retransmission from the retransmission start line number. Step S302 is an after-procedure. In the above embodiment, if the error retransmission mode is selected for communication over an international communication network, low speed transmission of image information is controlled to be performed from the called station to the calling station. However, besides such control method an error retransmission in a half duplex (so-called stop- and -wait error retransmission mode) may be applied. Furthermore, in the above embodiment although a depression of the international communication button is detected to judge whether communication is initiated, it is also possible to automatically judge initiation of an international communication by receiving initial identification signals NSF/CSI/DIS. As seen from the foregoing description of the third embodiment of the present invention, prior to sending and receiving data, the facsimile apparatus concerned can discriminate by itself whether it is a calling station or not. Therefore, it is possible to properly perform the succeeding transmission control procedure. For instance, if the error retransmission mode is selected for an international communication, data transmission from the calling station to the called station is performed in the error retransmission mode, while data transmission from the called station to the calling station is performed at low speed. Therefore, a disabled status in communication as conventional can be avoided even during data transmission from the called station to the calling station. As seen from the foregoing description of the present invention, data communication in a full duplex mode is possible. For instance, in case a reception error occurs during data communication, a continuous error retransmission mode informing the sending station of such effect can be effected using a conventional telephone network. The present invention is not intended to be limited to the above embodiments, but various applications and modifications are possible within the scope of the appended claims.

Claims: A data communication method for use on a communication network comprising the steps of: sending a communication procedure signal (S50-S62) prior to data communication and sending a data signal (S70), wherein the correct transmission of said data signal (S70) is controlled by means of a continuous error retransmission (S72-S76), said continuous error retransmission (S72-S76) can be suppressed by an echo suppressor function, said echo suppressor function can be stopped by a stop instruction (EST), and said stop instruction (EST) is released after a time interval during which no signal is generated, said method being characterized by further comprising the step of: sending a stop signal (S66) including said stop instruction (EST) for stopping said echo suppressor function, wherein said stop signal (S66) is sent prior to the communication of said data signal (S70) so that said time interval does not occur. A data communication method according to claim 1, being characterized in that said stop signal (S66) is sent in case where said data signal (S70) is sent under a continuous error retransmission mode. A data communication method according to claim 1, being characterized in that said stop signal (S66) is sent immediately before a training signal (S68) for a receiving station is sent. A data communication method according to claim 1, being characterized in that said stop signal (S66) is sent after receiving a signal (S76) indicating that a receiving station has prepared its reception. A data communication method according to claim 1, being characterized in that said data signal (S70) includes image information. A data communication apparatus comprising: data communication means (S70) for performing a data communication; pre-procedure means (S64) for performing a pre-procedure for the data communication; and interpage procedure means (S80) for performing, in a case where data communication of data corresponding to plural pages is performed by said data communication means (S70), a procedure or the data communication every time a communication of a page of data is completed, said apparatus being characterized by further comprising stop signal sending means for sending a stop signal (S66) to stop an echo suppressor function on a communication network immediately before the data communication (S70), in order to execute a communication in the pre-procedure (S64) and an interpage procedure (S80) in a half duplex mode and to execute the data communication (S70) in a full duplex mode. A data communication apparatus according to claim 6, being characterized in that said stop signal (S66) is sent in a case where said data signal (S70) is sent in a continuous error retransmission mode. A data communication apparatus according to claim 6, being characterized in that the stop signal (S66) is sent from a sending side. A data communication apparatus according to claim 6, being characterized in that said stop signal (S66) is sent immediately before sending of a training signal (S68), said training signal (S68) being sent prior to said data signal (S70), for training a reception apparatus. A data communication apparatus according to claim 6, being characterized in that said data signal (S70) includes image information. A data communication apparatus according to claim 6, being characterized by further comprising : discrimination means (S178; S294) for discriminating whether said data communication apparatus is a calling station or a called station; and control means (136; 240) for controlling such that said full duplex communication mode is selected to send the data signal (S184; S300) when said data communication is determined to be the calling station, and said half duplex communication mode is selected to send the data signal (S192; S288) when said data communication apparatus is discriminated to be the called station. A data communication apparatus according to claim 11, being characterized in that said full duplex communication mode includes a continuous error retransmission mode. A data communication apparatus according to claim 11, being characterized in that said discrimination means (S178; S294) performs discrimination prior to sending and receiving said data signal (S184, S192; S288, S300). A data communication apparatus according to claim 6, being characterized in that the data communication in said full duplex mode includes communication by continuous error retransmission. A data communication apparatus according to claim 6, being characterized in that data of the data communication includes image signal data. A data communication apparatus, comprising: first means for sending a communication procedure signal (S50-S60) via a communication network; second means for sending a data signal (S70) via the communication network; third means for sending, via the communication network, a training signal (S68) for training a reception apparatus prior to sending of the data signal (S70); and fourth means for receiving an error detection signal (NACK, S72-S76) from the reception apparatus during the data signal sending (S70) of said second means, said apparatus being characterized by further comprising fifth means for sending, via the communication network, a stop signal (S66) which includes a stop instruction (EST) for stopping an echo suppressor function on the communication network, wherein the stop signal (S66) is sent prior to the training signal (S68) sending by said third means, and a time interval between the training signal (S68) and the stop signal (S66) is set to be within a time required for restoring said echo suppressor function. A data communication apparatus according to claim 16, being characterized in that said stop signal (S66) is sent after said data communication apparatus receives from the reception apparatus a signal (S76) which indicates that preparation for signal reception at the reception apparatus is complete. A data communication apparatus according to claim 16, being characterized in that said data signal (S70) includes image information. A data communication apparatus according to claim 16, being characterized by further comprising retransmission means for re-sending the data signal (S70) when said error detection signal (NACK, S72-S76) is received by said fourth means, wherein said third means re-sends the training signal (S68) prior to the data signal (S70) re-sending by said retransmission means and said fifth means re-sends the stop signal (S66) immediately before the training signal (S68) re-sending by said third means.

Inventors: YOSHIDA, TAKEHIRO
Applicants: CANON KABUSHIKI KAISHA
Application year: 1986
Main classification: H04M11
IPC codes: H04N1, H04M11