Communication apparatus enabling communication according to ITU-T recommendation V.34

1. Field of the Invention

The present invention relates to a communication apparatus that enables communication, for example, in accordance with ITU-T Recommendation V.34.

2. Related Background Art

Conventionally, in the ITU-T V series of recommendations, retraining procedures are defined as a recovery operation that is to be performed for a communication error during the individual procedures.

However, while the definition for a retraining procedure via a control channel is included in, for example, the standards in the ITU-T Recommendations V.8 and V.34, it is not clear from which side a retrain signal should be transmitted when the procedure is to be actually executed. When a retrain signal is voluntarily transmitted from either side, the signals will conflict and the correct retrain procedures can not be performed.

To overcome the above problem, it is one object of the present invention to provide an improved communication apparatus.

It is another object of the present invention to appropriately perform retraining processing when communication errors occur on a control channel.

It is an additional object of the present invention to appropriately perform communication on a control channel.

The other objects of the present invention will become apparent during the course of the detailed description of the preferred embodiments, given while referring to the accompanying drawings.

FIG. 1 is a block diagram illustrating the arrangement of a facsimile machine according to a first and fourth to sixth embodiments of the present invention;

FIG. 2 is a flowchart showing the processing for the first embodiment;

FIG. 3 is a flowchart showing the processing for the first embodiment;

FIG. 4 is a flowchart showing the processing for the first embodiment;

FIG. 5 is a flowchart showing the processing for the first embodiment;

FIG. 6 is a flowchart showing the processing for the first embodiment;

FIG. 7 is a flowchart showing the processing for the first embodiment;

FIG. 8 is a flowchart showing the processing for the first embodiment;

FIG. 9 is a flowchart showing the processing for the first embodiment;

FIG. 10 is a flowchart showing the processing for the first embodiment;

FIG. 11 is a block diagram illustrating the arrangement of a facsimile machine according to a second and third embodiments of the present invention;

FIG. 12 is a flowchart showing the processing for the second embodiment;

FIG. 13 is a flowchart showing the processing for the second embodiment;

FIG. 14 is a flowchart showing the processing for the second embodiment;

FIG. 15 is a flowchart showing the processing for the third embodiment;

FIG. 16 is a flowchart showing the processing for the third embodiment;

FIG. 17 is a flowchart showing the processing for the fourth embodiment;

FIG. 18 is a flowchart showing the processing for the fourth embodiment;

FIG. 19 is a flowchart showing the processing for the fourth embodiment;

FIG. 20 is a flowchart showing the processing for the fourth embodiment;

FIG. 21 is a flowchart showing the processing for the fourth embodiment;

FIG. 22 is a flowchart showing the processing for the fourth embodiment;

FIG. 23 is a flowchart showing the processing for the fourth embodiment;

FIG. 24 is a flowchart showing the processing for the fourth embodiment;

FIG. 25 is a flowchart showing the processing for the fifth embodiment;

FIG. 26 is a flowchart showing the processing for the fifth embodiment;

FIG. 27 is a flowchart showing the processing for the fifth embodiment;

FIG. 28 is a flowchart showing the processing for the sixth embodiment;

FIG. 29 is a flowchart showing the processing for the sixth embodiment;

FIG. 30 is a flowchart showing the processing for the sixth embodiment;

FIG. 31 is a flowchart showing the processing for the sixth embodiment;

FIG. 32 is a flowchart showing the processing for the sixth embodiment;

FIG. 33 is a flowchart showing the processing for the sixth embodiment;

FIG. 34 is a flowchart showing the processing for the sixth embodiment;

FIG. 35 is a diagram for explaining retrain signal transmission timing according to the sixth embodiment; and

FIG. 36 is a diagram for explaining retrain signal transmission timing according to the sixth embodiment.

The preferred embodiments will now be described in detail while referring to the accompanying drawings.

A first embodiment of the present invention will now be explained.

In conventional facsimile communication according to the ITU-T Recommendations V.8 and V.34, a retrain signal in a control channel is defined. According to these recommendations, a retrain signal in a control channel can be dispatched by a transmitter to a receiver, or vice versa.

As a result, retrain signals will conflict with each other and the communication process can not be continued.

According to the first embodiment, a facsimile machine that can avoid the dispatch of conflicting retrain signals is provided.

FIG. 1 is a block diagram illustrating the arrangement of a facsimile machine according to the first embodiment of the present invention.

An NCU (Network Control Unit) 2 connects a telephone line to a terminal, controls the connection across the telephone network, selects a data communication channel and holds a loop, so as to employ a telephone network for data communication. When a signal level (signal line 20 a ) from a controller 20 is “0”, the NCU 2 connects a telephone line 2 a to a telephone set 4 . When the signal level is “1”, the NCU 2 connects the telephone line 2 a to a facsimile machine. In the normal state, the telephone line 2 a is connected to the telephone set 4 .

A hybrid circuit 6 separates a transmission system signal from a reception system signal, receives a signal from an adder circuit 12 that it transmits via the NCU 2 to the telephone line 2 a , and receives a signal from a partner via the NCU 2 that it transmits to a modem 8 along a signal line 6 a.

The modem 8 performs modulation and demodulation in accordance with the standards defined in ITU-T Recommendations V.8, V.21, V.27ter, V.29, V.17 and V.34, and the individual transfer modes are designated across a signal line 20 c . The modem 8 receives a signal via the signal line 20 b and outputs modulated data to a signal line 8 a , and receives a reception signal via the signal line 6 a and outputs demodulated data across a signal line 8 b.

An ANSam transmitting circuit 10 transmits an ANSam signal. When a signal at level “1” is output via the signal line 20 d , the ANSam transmitting circuit 10 transmits an ANSam signal across a signal line 10 a , but when a signal at level “0” is output across the signal line 20 d , the ANSam transmitting circuit 10 does not transmit any signal.

The adder circuit 12 adds data that are received via the signal lines 8 a and 10 a and outputs the results across a signal line 12 a . A reading circuit 14 reads a document image and outputs the image data across a signal line 14 a . A recording circuit 16 sequentially records data output for each line along a signal line 20 e.

A memory circuit 18 stores raw information or coded information for data that are read, or stores received information or decoded information.

A retraining direction setting circuit 22 sets a direction in which retraining is performed during communication via a control channel. When retraining from the transmitter to the receiver is selected, a signal at level “0” is output across the signal line 22 a . When retraining from the receiver to the transmitter is selected, a signal at level “1” is output across the signal line 22 a.

A control circuit 20 controls the facsimile communication function defined in ITU-T Recommendations V.8 and V.34. The control circuit 20 performs a pre-procedure to determine direction in which a retrain signal is to be transmitted when communicating across (or via) the control channel, and in accordance with this determination, employs the retraining as needed while the communicating across (or via) the control channel.

At the pre-procedure, whether the transmitter can transmit a retrain signal while communicating across the control channel, and whether it can receive a retrain signal from the receiver when communicating across the control channel, are transmitted to the receiver by the transmitter. Upon receipt of this notification, the receiver notifies the transmitter whether the retrain signal is transmitted to the transmitter or received from the transmitter while communicating across the control channel.

In this manner, the retrain signal dispatched while the communication is taking place across the control channel is determined to be either a transmission from the transmitter to the receiver, or a transmission from the receiver to the transmitter. The control circuit 20 is mainly responsible for performing the above processing.

FIGS. 2 to 10 are flowcharts showing the control processing performed by the control circuit 20 according to the first embodiment of the present invention.

In FIG. 2, the control circuit 20 is activated at step S 0 , and at step S 2 , outputs a signal at level “0” to the signal line 20 a and turns off a CML. At step S 4 the control circuit 20 outputs a signal at level “0” to the signal line 20 d to set an ANSam signal non-transmission state.

At steps S 6 and S 8 , checks are sequentially performed to determine whether reception or transmission is selected. When reception is selected, program control moves to step S 12 , and when transmission is selected, program control goes to step S 104 . When neither of them is selected, program control goes to step S 10 , whereat the other process is performed. Program control thereafter returns to step S 2 .

At step S 12 , a signal at level “1” is output to the signal line 20 a and the CML is turned on. At step S 14 , an ANSam signal is output and at step S 16 a CM signal is received. At this time, information is stored concerning whether or not the transmitter can transmit a retrain signal to the receiver while communicating across the control channel and whether or not the transmitter can receive a retrain signal from the receiver while communicating across the control channel.

At step S 18 , information carried on the signal line 22 a is received, and a check is performed to determine whether transmission of the retrain signal from the transmitter to the receiver has been selected. When transmission of the retrain signal from the transmitter to the receiver has been selected, program control advances to step S 20 . When transmission from the receiver to the transmitter has been selected, program control goes to step S 32 .

At step S 20 , the information concerning the CM signal, which is received at step S 16 , can be employed to determine whether or not a partner's station is capable of performing the retrain process in a direction from the transmitter to the receiver. If the partner's station has that capability, program control moves to step S 22 ; if not, program control moves to step S 26 .

At step S 22 , transmission of a JM signal is executed. With the JM signal, the retraining of the control channel from the transmitter to the receiver is designated for the partner's station. At step S 24 , a CJ signal is received and program control advances to step S 40 .

At step S 26 , the information concerning the CM signal, which is received at step S 16 , can be employed to determine whether or not a partner's station is capable of performing the retrain process in a direction from the receiver to the transmitter. If the partner's station has that capability, program control advances to step S 28 ; if not, program control moves to step S 36 .

At step S 28 , transmission of a JM signal is executed. With the JM signal, transmission of the retrain signal across the control channel from the transmitter to the receiver is designated for the partner's station. At step S 30 , a CJ signal is received and program control advances to step S 64 .

At step S 32 , the information concerning the CM signal, which is received at step S 16 , can be employed to determine whether or not the partner's station is capable of performing the retrain process in a direction from the receiver to the transmitter. If the partner's station has that capability, program control advances to step S 28 ; if not, program control moves to step S 34 .

At step S 34 , the information concerning the CM signal, which is received at step S 16 , can be employed to determine whether or not the partner's station is capable of performing the retrain process in a direction from the transmitter to the receiver. If the partner's station has that capability, program control advances to step S 22 ; if not, program control moves to step S 36 .

At step S 36 , transmission of a JM signal is executed. With the JM signal, the transmission of the retrain signal across the control channel from the transmitter to the receiver is designated for the partner's station. At step S 38 , a CJ signal is received and program control advances to step S 90 .

The reception of a line probing signal at step S 40 , the reception of a long training signal at step S 42 , the exchange of parameters at step S 44 , the reception of primary channel data at step S 46 , and the initiation of communication across a V.34 control channel at step S 48 are performed.

At step S 50 , a check is performed to determine whether an AC signal has been detected, i.e., whether a retrain signal across the control channel is detected. When an AC signal is detected, program control advances to step S 52 . If an AC signal has not been detected, program control moves to step S 60 .

Transmission and reception of a PPh signal at step S 52 , transmission and reception of an ALT signal at step S 54 , transmission and reception of an MPh signal at step S 56 , and transmission and reception of an E signal at step S 58 are performed.

At step S 60 , a check is performed to determine whether the procedures conforming to V.34 have been completed. When the procedures have been terminated, program control moves to step S 62 , and when they have not yet been completed, program control moves to step S 48 .

At step S 62 , a check is performed to determine whether there is a subsequent page. If there is a subsequent page, program control advances to step S 46 , and if there are no more pages, program control moves to step S 2 .

The reception of a line probing signal at step S 64 , the reception of a long training signal at step S 66 , and the communication across V.34 control channel at step S 72 are performed.

At step S 74 , a check is performed to determine whether a procedure error has occurred during communication through the control channel. When a procedure error has occurred, program control moves to step S 76 , and when no error has occurred, program control goes to step S 86 .

At step S 76 , transmission of an AC signal is executed to execute retraining across the control channel. Then, reception and transmission of an ALT signal at step S 80 , reception and transmission of an MPh signal at step S 82 , and reception and transmission of an E signal at step S 84 are performed.

At step S 86 , a check is performed to determine whether the processing defined in V.34 has been terminated. When the processing has been terminated, program control moves to step S 88 . When the processing has not yet been terminated, program control goes to step S 72 . At step S 88 , a check is performed to determine whether there is a subsequent page. If there is a subsequent page, program control returns to step S 70 , and if not, program control returns to step S 2 .

The reception of a line probing signal at step S 90 , the reception of a long training signal at step S 92 , and the exchange of parameters at step S 94 , and the reception of V.34 primary channel information at step S 96 are performed.

At step S 98 , communication across the V.34 control channel is performed. An AC signal is neither transmitted nor received, i.e., the retraining across the control channel is not performed.

Following this, at step S 100 a check is performed to determine whether the procedure defined in V.34 has been terminated. If the procedure defined in V.34 has been terminated, program control advances to step S 102 . If the procedure has not yet been terminated, program control returns to step S 98 . At step S 102 , a check is performed to determine whether there is a subsequent page. If there is a subsequent page, program control returns to step S 96 , and if not, program control returns to step S 2 .

At step S 104 , a signal at level “1” is output along the signal line 20 a to turn on the CML. At step S 106 , an ANSam signal is received.

At step S 108 , transmission of a CM signal is executed. At this time, information is transmitted concerning whether the transmitter can transmit a retrain signal while communicating across the control channel and whether the transmitter can receive a retrain signal from the receiver while communicating across the control channel (for example, information indicating that both capabilities exist).

At step S 110 , a JM signal is received, and the retraining information in a control channel designated by the partner's station is stored.

Following this, the transmission of a CJ signal at step S 112 , the transmission of a line probing signal at step S 114 , the transmission of a long training signal at step S 116 and the exchange of parameters at step S 118 are sequentially performed.

At step S 120 , the retraining signal transmitted across the control channel designated by the JM signal is examined. When the performance of the retrain process from the transmitter to the receiver is selected, program control advances to step S 122 . When the performance of the retrain process from the receiver to the transmitter is selected, program control moves to step S 142 . When the performance of the retrain process across the control channel is not selected, program control goes to step S 160 .

At step S 122 , V.34 primary channel information is transmitted, and at step S 124 , communication across the control channel is executed.

At step S 126 , a check is performed to determine whether a procedure error has occurred while communication across the control channel is in progress. When a procedure error has occurred, program control advances to step S 128 . When a procedure error has not occurred, program control moves to step S 138 .

At step S 128 , an AC signal is transmitted to perform retraining across the control channel. The reception and transmission of a PPh signal at step S 130 , the reception and transmission of an ALT signal at step S 132 , the reception and transmission of an MPh signal at step S 134 , and the reception and transmission of an E signal at step S 136 are performed.

At step S 138 , a check is performed to determine whether the procedure defined in V.34 has been terminated. If the procedure defined in V.34 has been terminated, program control advances to step S 140 . If the procedure has not yet been terminated, program control returns to step S 124 . At step S 140 , a check is performed to determine whether there is a subsequent page. If there is a subsequent page, program control returns to step S 122 ; if not, program control returns to step S 2 .

At step S 142 , V.34 primary channel information is transmitted, and at step S 144 , communication across the control channel is executed.

At step S 146 , a check is performed to determine whether an AC signal has been detected, i.e., whether transmission of a retrain signal across the control channel has been detected. When an AC signal has been detected, program control advances to step S 148 , and when an AC signal has not been detected, program control moves to step S 156 .

Following this, the transmission and reception of a PPh signal at step S 148 , the transmission and reception of an ALT signal at step S 150 , the transmission and reception of an MPh signal at step S 152 , and the transmission and reception of an E signal at step S 154 are sequentially performed.

At step S 156 , a check is performed to determine whether the procedure defined in V.34 has been terminated. If the procedure defined in V.34 has been terminated, program control advances to step S 156 . If the procedure has not yet been terminated, program control returns to step S 144 . At step S 158 , a check is performed to determine whether there is a subsequent page. If there is a subsequent page, program control returns to step S 142 ; if not, program control returns to step S 2 .

At step S 160 , V.34 primary channel information is transmitted, and at step S 162 , communication across the control channel is executed. An AC signal is neither transmitted nor received, i.e., the retraining process is not performed across the control channel.

At step S 164 , a check is performed to determine whether the procedure defined in V.34 has been terminated. If the procedure defined in V.34 has been terminated, program control advances to step S 166 . If the procedure has not yet been terminated, program control returns to step S 162 . At step S 166 , a check is performed to determine whether there is a subsequent page. If there is a subsequent page, program control returns to step S 160 ; if not, program control returns to step S 2 .

A second embodiment for the present invention will now be described.

For the above described facsimile machine that can perform communication according to ITU-T Recommendations V.8 and V.34, as V.34 control channel signals there are signals PPh, ALT, MPh, Sh, Sh * , E, etc. Signal Sh * is a phase-inverted Sh signal, and in the drawings is presented by an Sh.

Conventionally, the baud rate for the signals PPh, Sh, Sh * and E are fixed, and while an ALT signal from the reception modem ranges from 16 baud to 120 baud, 16 baud is selected as the fixed value in order to effect a reduction in communication time.

However, the recovery procedures for individual information transmitted across a V.34 control channel are not defined in the current ITU-T Recommendation, and it is presumed that the receipt by a partner's station a signal transmitted by a concerned station is ensured.

Retraining using an AC signal is determined as constituting a recovery performed via the entire V.34 control channel. However, since there is no recovery procedure for individually transmitted information, according to the current Recommendation the performance via the V.34 control channel must be ensured, otherwise a problem with communication occurs on the V.34 control channel and a transfer across a fast primary channel can not be effectively performed.

In the second embodiment of the present invention, therefore, provided is a facsimile machine that can appropriately control the baud rate for an ALT signal transmitted by a reception modem, that can give priority to high speed communication when a reception level is high, and give priority to communication certainty when a reception level is low, and that can provide an improved communication success rate via a V.34 control channel. According to a third embodiment of the present invention, provided is a facsimile machine that changes a detection condition at a reception side via the V.34 control channel so as to provide an improved communication success rate, even when the reception level is low.

FIG. 11 is a block diagram illustrating a facsimile machine according to the second and the third embodiment of the present invention.

An NCU (Network Control Unit) 102 connects a telephone line to a terminal, controls the connection across the telephone network, selects a data communication channel, and holds a loop, so as to employ a telephone network for data communication. When a signal level (signal line 120 a ) from a controller 120 is “0”, the NCU 102 connects a telephone line 102 a to a telephone set 104 . When the signal level is “1”, the NCU 102 connects the telephone line 102 a to a facsimile machine. In the normal state, the telephone line 102 a is connected to the telephone set 104 .

A hybrid circuit 106 separates a transmission system signal from a reception system signal, receives a signal from an adder circuit 112 and transmits it via the NCU 102 to the telephone line 102 a , and receives a signal from a partner via the NCU 102 and transmits it to a modem 108 along a signal line 106 a.

The modem 108 performs modulation and demodulation in accordance with the standards defined in ITU-T Recommendations V.8, V.21, V.27ter, V.29, V.17 and V.34, and the individual transfer modes are designated across a signal line 120 c . The modem 108 receives a signal from the signal line 120 b and outputs modulated data to a signal line 108 a , and receives a reception signal from the signal line 106 a and outputs demodulated data to a signal line 108 b.

An ANSam transmitting circuit 110 transmits an ANSam signal. When a signal at level “1” is output to the signal line 120 d , the ANSam transmitting circuit 110 transmits an ANSam signal across a signal line 110 a , but when a signal at level “0” is output to the signal line 120 d , the ANSam transmitting circuit 110 does not transmit any signal.

The adder circuit 112 adds data that are received via the signal lines 108 a and 110 a and outputs the results across a signal line 112 a . A reading circuit 114 reads a document image and outputs the image data across a signal line 114 a . A recording circuit 116 sequentially records data output for each line along a signal line 120 e.

A memory circuit 118 stores raw information or coded information for data that are read, or stores received information or decoded information.

A reception level detection circuit 122 receives information via the signal line 106 a and outputs a current reception level across a signal line 122 a.

A control circuit 120 controls the facsimile communication function defined in ITU-T Recommendations V.8 and V.34, especially in the second embodiment. Based on the reception level detected by the reception level detection circuit 122 , the control circuit 120 changes the baud rate when an ALT signal originating at the reception modem is to be transmitted across the V.34 control channel. When the reception level is low, the baud rate is increased for the transmission across the V.34 control channel of an ALT signal originating at the reception modem. When the reception level is high, the baud rate is decreased for the transmission across the V.34 control channel of an ALT signal originating at the reception modem.

FIGS. 12 to 14 are flowcharts showing the control processing performed by the control circuit 120 in the second embodiment.

In FIG. 12, the control circuit 120 is activated at step S 200 , and at step S 202 , it outputs a signal at level “0” across the signal line 120 a and turns off a CML. At step S 204 , the control circuit 120 outputs a signal at level “0” across the signal line 120 d to set an ANSam signal no-transmission state.

At step S 206 , a check is sequentially performed to determine whether reception has been selected. When reception has been selected, program control moves to step S 210 , and when reception has not been selected, program control goes to step S 208 and the other process is performed. Program control thereafter moves to step S 202 .

At step S 210 , a signal at level “1” is output across the signal line 120 a and the CML is turned on. Then, the transmission of an ANSam signal at step S 212 , reception of a CM signal at step S 214 , the transmission of a JM signal at step S 216 , and the reception of a CJ signal at step S 218 are sequentially performed.

Following this, the reception of a line probing signal at step S 220 and the reception of a long training signal at step S 222 are performed. At this time, information transmitted across the signal line 122 a is received and the reception level is stored.

Sequentially, the exchange of parameters at step S 224 , the reception of primary channel information at step S 226 , and the initiation of communication via the V.34 control channel at step S 228 are performed. When Sh and Sh * signals are detected, program control moves to step S 230 . When a PPh signal is detected, program control goes to step S 250 .

At steps S 234 and S 236 , the reception level stored at step S 222 is examined. If the reception level is equal to or higher than −20 dBm, program control advances to step S 238 . If the reception level is equal to or higher than −30 dBm and is less than −20 dBm, program control moves to step S 240 . If the reception level is less than −30 dBm, program control goes to step S 242 .

The transmission and reception of an ALT signal (16 baud) at step S 238 , the transmission and reception of an ALT signal (50 baud) at step S 240 or the transmission and reception of an ALT signal (120 baud) at step S 242 is performed.

At step S 244 , the reception and transmission of an E signal are performed, and at step S 248 , a check is performed to determine whether there is a subsequent page. If there is a subsequent page, program control returns to step. S 226 ; if there are no more pages, program control returns to step S 202 .

At step S 250 , a PPh signal (32 baud) is transmitted, and at steps S 252 and S 254 , the reception level stored at step S 222 is examined. If the reception level is equal to or higher than −20 dBm, program control advances to step S 256 . If the reception level is equal to or higher than −30 dBm and less than −20 dBm, program control moves to step S 258 . If the reception level is less than −30 dBm, program control goes to step S 260 .

The transmission and reception of an ALT signal (16 baud) at step S 256 , the transmission and reception of an ALT signal (50 baud) at step S 258 or the transmission and reception of an ALT signal (120 baud) at step S 260 is performed. At step S 262 , the reception and transmission of an MPh signal is performed, and program control returns to step S 244 .

The third embodiment of the present invention will now be described.

In the third embodiment, in FIG. 11, based on the reception level detected by the reception level detection circuit 122 , the control circuit 120 changes the baud rate for the transmission of signals Sh, Sh * and PPh via the V.34 control channel, the number of MPh the signals in the V.34 control channel, and the bit count for an E signal is the V.34 control channel.

When a signal is received via the V.34 control channel, in accordance with the reception level, the control circuit 120 changes the number of the signals the detection of which is ascertained. Specifically, when the reception level is low, the number of the signals in the V.34 control channel, the detection of which is ascertained, is reduced. When the reception level is high, the number of the signals in the V.34 control channel, the detection of which is ascertained, is increased.

FIGS. 15 and 16 are flowcharts showing the control exercised by the control circuit 120 in the third embodiment, and only those portions that differ from the portions in the second embodiment (FIGS. 12 to 14 ) are shown.

In FIG. 15, step S 270 corresponds to step S 226 . At step S 272 , a signal transmitted across the signal line 122 a is received, and a check is performed to determine whether the reception level is equal to or higher than −30 dBm. If the reception level is equal to or higher than −30 dBm, program control advances to step S 274 , and if the reception level is less than −30 dBm, program control moves to step S 292 .

At step S 274 , a check is performed to determine whether two sets of signals Sh and Sh * are detected, or two PPh signals are detected. When two sets of Sh and Sh * signals are detected, program control advances to step S 276 . When two PPh signals are detected, program control moves to step S 286 .

At step S 276 , Sh signal (24 baud) is transmitted, at step S 278 , Sh * signal (8 baud) is transmitted, and at step S 280 an ALT signal (50 baud) is transmitted. At the same time, the reception of ALT signals is executed, and when two ALT signals have been received, an acceptable reception is established.

At step S 282 , reception of an E signal is excuted, and when “1”s of five bits or more have been received, an acceptable reception is established. At the same time, transmission of an E signal (“1”s of 20 bits) is executed. Thereafter, program control moves to step S 246 at step S 284 .

At step S 286 , transmission of a PPh signal (32 baud) is executed, and at step S 288 , transmission of an ALT signal (50 band) is executed. At the same time, reception of ALT signal is executed and when two ALT signals have been received, an acceptable reception is established.

At step S 290 , reception of MPh signals is executed, and when two MPh signals have been received, an acceptable reception is established. Transmission of MPh signals is also performed. At least three MPh signals are to be transmitted, and the MPh signal transmission is continued until an acceptable reception of the MPh signals is established. Program control thereafter moves to step S 282 .

At step S 292 , a check is performed to determine whether signals Sh and Sh * have been detected or a PPh signal has been detected. When a signal Sh and a signal Sh * are detected, program control advances to step S 294 . When one PPh signal is detected, program control moves to step S 304 .

At step S 294 , Sh signals (48 baud) are transmitted, at step S 296 , Sh * signals (16 baud) are transmitted, and at step S 298 , an ALT signal (120 baud) is transmitted. At the same time, reception of an ALT signal is executed, and when one ALT signal is received, reception OK is established.

At step S 300 , reception of an E signal is executed, and when “1”s of three bits or more have been received, an acceptable reception is established. Transmission of an E signal (one of 40 bits) is also performed. Program control moves from step S 302 to step S 246 .

At step S 304 , a PPh signal (64 baud) is transmitted, and at step S 306 , an ALT signal (120 baud) is transmitted. At the same time, reception of an ALT signal is executed, and when one ALT signal has been received, an acceptable reception is established.

At step S 308 , reception of an MPh signal is executed, and when one MPh signal has been received, an acceptable reception is established. Transmission of an MPh signal is also performed. At least three signals are to be transmitted, and the transmission of the MPh signals continues until an acceptable reception is established. Program control thereafter moves to step S 300 .

A fourth embodiment according to the present invention will now be described.

As is described above, the designation (or execution) of retrain (sequence) via the control channel is not defined in detail in ITU-T Recommendation V.8 and V.34, and varies depending on the maker. However, since it is difficult to designate the retrain (sequence) via the control channel, to count the number of instructions transmitted in response to the detection of retrain (signal) via the control channel, and to regulate various timers, there is no guarantee that satisfactory communications can be established.

In the fourth embodiment, provided is a facsimile machine that can be easily designed without taking into consideration the total number of re-transmissions of command signals theretofore when the retrain is designated or detected via the control channel, or the elapse of time according to various timers (a timer T 4 , a timer T 2 , etc.); that can improve the effectiveness of the design and communication continuation reliability; and that provides a clear condition for halting repetitious processing due to continuous retraining performed across the control channel.

Since the arrangement of the facsimile machine in the fourth embodiment is the same as that shown in FIG. 1, the following explanation will be given while referring to FIG. 1 .

A control circuit 20 in the fourth embodiment exercises the following control. When a retrain is designated or detected via the control channel during the conduct of communications conforming to the ITU-T Recommendations V.8 and V.34, the control circuit 20 shifts to the initial state for transmission/reception via the control channel. When the total count of designations and detections of the retrains via the control channel is equal to or greater than a predetermined number (e.g., four or more), the control circuit 20 discontinues the communication.

During the reception of a response, when the retrain is designated or detected via the control channel, the control circuit 20 clears a three-count re-transmission counter for a command signal, and shifts to the transmission of control channel data to transmit a command signal. During the reception of a command signal, when the retrain is designated or detected, the control circuit 20 clears a timer T 2 when it shifts to the reception of control channel data.

FIGS. 17 to 24 are flowcharts showing the control processing performed by the control circuit 20 in the fourth embodiment.

An explanation will be given for response reception after a PPS-Q has been transmitted following the transmission of primary channel information, and command reception after primary channel information has been received.

In FIG. 17, the control circuit 20 is activated at step S 400 , and at step S 402 outputs to the signal line 20 a a signal at level “0” and turns off a CML. At step S 404 , the control circuit 20 outputs a signal at level “0” to the signal line 20 d to set an ANSam signal nontransmission state.

At steps S 406 and S 408 , a check is performed to determine whether reception or transmission has been selected. When reception has been selected, program control moves to step S 412 , and when transmission has been selected, program control goes to step S 476 . When neither of them has been selected, program control moves to step S 410 , whereat the other process is performed. Thereafter, program control returns to step S 402 .

At step S 412 , a signal at level “1” is output to the signal line 20 a and the CML is turned on. Following this, the transmission of an ANSam signal at step S 414 , the reception of a CM signal at step S 416 , transmission of a JM signal at step S 418 , the reception of a CJ signal at step S 420 , the reception of a line probing signal at step S 422 , the reception of a long training signal at step S 424 , the exchange of parameters at step S 426 , and the reception of primary channel information at step S 428 are sequentially performed.

At step S 430 , a counter AC counter, which acquires the sum of designations and detections of the retrains, is cleared. At step S 432 , the transmission/reception of a V.34 control channel signal is performed, and at step S 434 , a timer Timer is set as six seconds for the detection of control channel data.

At step S 436 , either the transmission/reception of signals Sh, Sh * , ALT and E, or the transmission/reception of signals PPh, ALT, MPh and E is performed.

At step S 438 , a check is performed to determine whether or not control channel data have been detected. When control channel data have been detected, program control moves to step S 460 , and when control channel data have not been detected, program control advances to step S 440 . At step S 440 , a check is performed to determine whether an AC signal (retrain) is detected. If an AC signal has been detected, program control moved to step S 444 , whereat the value of the AC counter is incremented by one. If an AC signal has not been detected, program control goes to step S 442 .

At step S 442 , a check is performed to determine whether the Timer times out. When the Timer times out, program control advances to step S 443 , whereat an AC signal is transmitted to designate the retrain. If the Timer dose not time out, program control moves to step S 436 .

At step S 446 , a check is performed to determine whether the count of the AC counter is four or greater, i.e., whether the sum of designations and detections of the retains is four or greater. When the sum is four or greater, program control moves to step S 448 , whereat an error due to an AC signal is stored. When the sum is less than four, program control goes to step S 450 .

At step S 450 , the timer Timer is set as six seconds for the detection of control channel data. At step S 452 , transmission/reception of signals PPh, ALT, MPh and E is performed.

At step S 454 , a check is performed to determine whether control channel data have been detected. If control channel data have been detected, program control moves to step S 460 . When control channel data have not been detected, program control advances to step S 456 .

At step S 456 , a check is performed to determine whether or not an AC signal (retrain) has been detected. If an AC signal has been detected, program control returns to step S 444 , and if an AC signal has not been detected, program control advances to step S 458 . At step S 458 , a check is performed to determine whether the Timer times out. When the Timer times out, program control advances to step S 443 and when the Timer does not time out, program control moves to step S 452 .

At step S 460 , a timer T 2 is set as six seconds, and at step S 462 a check is performed to determine whether a PPS-Q signal has been received. When a PPS-Q signal has been received, program control advances to step S 472 , whereat the transmission/reception of a V.34 control channel signal is executed. When a PPS-Q signal has not been received, program control moves to step S 464 .

At step S 464 , a check is performed to determine whether or not an AC signal (retrain) has been detected. If an AC signal has been detected, program control returns to step S 444 , and if an AC signal has not been detected, program control advances to step S 466 .

At step S 466 , a check is performed to determine whether for a period of one second or more there has been no flag detected. If no flag has been detected for one second or longer, program control returns to step S 443 . If no flag has been detected for less than one second, program control goes to step S 468 .

At step S 468 , a check is performed to determine whether the T 2 timer times out. When the timer does not time out, program control advances to step S 462 , and when the timer times out, program control moves to step S 470 , whereat an error process is performed. Program control thereafter returns to step S 402 .

At step S 474 , a check is performed to determine whether the next partial page is to be received. If the decision is YES, program control returns to step S 428 , but if the decision is NO, program control returns to step S 402 .

At step S 476 , a signal at a level “1” is output to the signal line 20 a and the CML is turned on. Following this, the transmission of an ANSam signal at step S 478 , the reception of a JM signal at step S 482 , the transmission of a CJ signal at step S 484 , the transmission of a line probing signal at step S 485 , the transmission of a long training signal at step S 486 , the exchange of parameters at step S 488 , and the transmission of primary channel information at step S 490 are performed.

At step S 492 , a counter (AC counter), which acquires the sum of designations and detections of the retrains via the control channel, is cleared.

At step S 494 , the transmission/reception of a V.34 control channel signal is executed, and at step S 496 a three-count re-transmission counter Counter for a PPS-Q signal is cleared. At step S 498 , the timer Timer is set as six seconds for the detection of control channel data, and at step S 500 , the transmission/reception of signals Sh, Sh * , ALT and E, or the transmission/reception of signals PPh, ALT, MPh and E, is performed.

At step S 502 , a check is performed to determine whether or not control channel data have been detected. When control channel data have been detected, program control moves to step S 526 , and when control channel data have not been detected, program control advances to step S 504 .

At step S 504 , a check is performed to determine whether an AC signal (retrain) has been detected. If an AC signal has been detected, program control moves to step S 508 , whereat the value of the AC counter is incremented by one. If an AC signal has not been detected, program control goes to step S 506 .

At step S 506 , a check is performed to determine whether the Timer times out. When the Timer does not time out, program control returns to step S 500 . If the Timer times out, program control moves to step S 507 , whereat an AC signal is transmitted to designate the retrain.

At step S 510 , a check is performed to determine whether the count of the AC counter is four or greater, i.e., whether the sum of designations and detections of the retains is four or greater. When the sum is four or greater, program control moves to step S 512 , whereat an error due to an AC signal is stored. When the sum is less than four, program control goes to step S 514 , whereat the three-count PPS-Q re-transmission counter Counter is cleared.

At step S 516 , the timer Timer is set as six seconds for the detection of control channel data. At step S 518 , the transmission/reception of signals PPh, ALT, MPh and E is performed.

At step S 520 , a check is performed to determine whether control channel data have been detected. If control channel data have been detected, program control moves to step S 526 . When control channel data have not been detected, program control advances to step S 522 . At step S 522 , a check is performed to determine whether or not an AC signal (retrain) has been detected. If an AC signal has been detected, program control returns to step S 508 , and if an AC signal has not been detected, program control advances to step S 524 .

At step S 524 , a check is performed to determine whether the Timer times out. When the Timer times out, program control returns to step S 507 , but when the Timer does not time out, program control returns to step S 518 .

At step S 526 , the transmission of a preamble 100 mS is executed, and at step S 528 , a PPS-Q signal is transmitted. At step S 530 , a timer T 4 is set as three seconds, and at step S 532 , a check is performed to determine whether one signal of an MCF, a PPR, and an RNR has been detected. When one of these signals has been detected, program control moves to step S 534 , whereat the transmission/reception via the V.34 control channel is executed. Program control thereafter advances to step S 536 . When none of the signals has been detected, program control advances to step S 538 .

At step S 536 , a check is performed to determine whether the next partial page is to be transmitted. If the decision is YES, program control returns to step S 490 , and if the decision is NO, program control returns to step S 402 .

At step S 538 , a check is performed to determine whether an AC signal (retrain) has been detected. If an AC signal has been detected, program control moves to step S 508 , and if an AC signal has not been detected, program control goes to step S 540 .

At step S 540 , a check is performed to determine whether for a period of one second or more there has been no flag detected. If no flag has been detected for one second or longer, program control returns to step S 507 . If no flag is detected for less than one second, program control goes to step S 542 .

At step S 542 , a check is performed to determine whether the T 4 timer times out. When the timer does not time out, program control returns to step S 532 and when the timer times out, program control advances to step S 544 , whereat the value of the PPS-Q re-transmission counter Counter is incremented by one.

At step S 546 , a check is performed to determine whether the count of the PPS-Q re-transmission counter Counter is three or greater. When the count is three or greater, program control advances to step S 548 , and when the count is less than three, program control returns to step S 526 .

Then, the transmission of preamble 100 mS at step S 548 , the transmission of a DCN signal at step S 550 , and an error process at step S 552 are sequentially performed. Program control thereafter returns to step S 402 .

As a modification of the above described fourth embodiment, the same processing may be performed at timings other than those for the response reception and the command reception.

A fifth embodiment according to the present invention will now be described.

In the above described ITU-T Recommendations V.8 and V.34, there are no rules either concerning the how to use carrier detection, which a modem outputs as a status as to whether a significant signal has been received from a partner's station, or concerning designation of the retrain via a control channel.

Since a control channel for communication conforming to the ITU-T Recommendations V.8 and V.34 is of full-duplex, and a primary channel is of half-duplex, the reliability of the carrier detection signals differs. Specifically, the carrier detection in communication via the control channel is less reliable because of full-duplex. If the retrain is effected via the control channel based on the carrier detection, the retrain is executed even though the reception data are correctly demodulated, sequently resulting in a communication error.

In the fifth embodiment of the present invention, provided is a facsimile machine that, in full-duplex communications via the control channel, shifts to the retrain process by rendering OFF less reliable carrier detection, and holds the communication.

Since the arrangement of the facsimile machine in the fifth embodiment is the same as that in FIG. 1, an explanation will be given while referring to FIG. 1 . It should be noted that a control circuit 20 in the fifth embodiment exercises the following control.

When the control circuit 20 is to be shifted to the transmission of control channel data while engaging in the communications via the control channel that conforms to the ITU-T Recommendations V.8 and V.34, the control channel retrain process is inhibited by rendering OFF the carrier detection that indicates the detection of control channel data from the partner's station. When a procedure signal is not detected within a predetermined period of time (e.g., 1.3 seconds) or longer while communicating across the control channel, the control circuit 20 designates the retrain.

The 1.3 seconds (set to a timer) are obtained by adding a detection time of 0.1 second to a line delay of 1.2 seconds.

During the reception via the primary channel, when the control circuit 20 detects the OFF state of the carrier detection, it shifts to reception via the control channel. Specifically, when the reception via the primary channel is begun, the rendering ON of the carrier detection need only be confirmed within 1.3 seconds. Once the control circuit 20 detects the ON state of the carrier detection, it shifts to reception via the control channel in response to the rendering OFF of consecutive carrier detection for 40 mS or longer.

The 1.3 seconds (set to a timer) at the beginning of the reception of primary channel data are also obtained by adding a detection time of 0.1 second to a line delay of 1.2 seconds.

Since a no-tone interval between the primary channel and the control channel is 70 mS±5 mS, once the carrier detection for the primary channel data has been detected, a carrier disconnection of 40 mS is detected and the control circuit 20 is shifted from the reception of primary channel data to the reception of control channel data.

FIGS. 25 to 27 are flowcharts showing the control processing performed by the control circuit 20 in the fifth embodiment.

In FIG. 25, the control circuit 20 is activated at step S 600 , and at step S 602 , outputs a signal at level “0” to the signal line 20 a and turns off a CML. At step S 604 , the control circuit 20 outputs a signal at level “0” to the signal line 20 d to set an ANSam signal non-transmission state.

At steps S 606 , a check is performed to determine whether reception is selected. When reception is selected, program control moves to step S 610 , and when it is not selected, program control moves to step S 608 , whereat the other process is performed. Program control thereafter returns to step S 602 .

At step S 610 , a signal at level “1” is output to the signal line 20 a and the CML is turned on. Following this, the transmission of an ANSam signal at step S 612 , the reception of a CM signal at step S 614 , transmission of a JM signal at step S 616 , the reception of a CJ signal at step S 618 , the reception of a line probing signal at step S 620 , the reception of a long training signal at step S 622 , and the exchange of parameters at step S 624 are sequentially performed.

At step S 626 , a CD OFF timer is set as 1.3 seconds by taking into account a line delay of 1.2 seconds and a detection time of 0.1 second. At step S 628 , in order to guarantee reception of control data after a momentary disconnection occurs in case one partial page has 256 frames, 256 frames each having 269 bytes that is the sum of 256 bytes for one frame data, 8 bytes for A, C, FCF, Frame No., FCS, FCS, F and F, and an extra 5 bytes, are divided by a transfer speed, the resultant value is stored in the timer, and the reception of control channel data is continued until the CD-OFF timer times out following the momentary disconnection.

At step S 630 , the primary channel data are received, and at step S 632 , the status (carrier detection) via the modem, which indicates that the primary channel data have been received, is examined. When the carrier detection is in the ON state, program control advances to step S 634 , whereat 40 mS is set to the CD OFF timer. When the carrier detection is OFF, program control moves to step S 636 .

At step S 636 , a check is performed to determine whether the CD OFF timer times out. When the timer times out, program control advances to step S 642 , whereat the process is shifted to the reception of control channel data. If the timer does not time out, program control goes to step S 638 .

At step S 638 , a check is performed to determine whether or not an RCP signal has been detected. If an RCP signal has been detected, program control advances to step S 640 , whereat 20 seconds are set to a timer for transmission of control channel data. Program control thereafter advances to step S 642 . If an RCP signal has not been detected, program control returns to step S 630 .

At step S 642 , the transmission/reception of V.34 control channel data is executed, and at step S 644 a check is performed to determine whether a concerned station has been shifted to the transmission of control channel data. When the station has been shifted to the transmission of control channel data, program control advances to step S 646 , and when the station has not been shifted to the transmission of control channel data, program control returns to step S 642 .

At step S 646 , 1.3 seconds are set to a control timer. As previously described, the period of 1.3 seconds are obtained by adding a line delay of 1.2 seconds to a detection time of 0.1 second. At step S 648 , the transmission/reception of control channel data is executed.

At step S 650 , a check is performed to determine whether a significant signal, such as a PPS-Q signal, can be detected among the control channel data. If a significant signal is detected, program control moves to step S 654 , and if a significant signal is not detected, program control advances to step S 652 .

At step S 652 , a check is performed to determine whether or not two consecutive flags for control channel data have been detected. When two such flags have been detected, program control moves to step S 654 , whereat 1.3 seconds are set to the control timer. When two consecutive flags have not been detected, program control advances to step S 656 .

At step S 656 , a check is performed to determine whether the transmission via the control channel has been terminated. If the transmission via the control channel has been terminated, program control goes to step S 658 , and if the transmission has not been terminated, program control advances to step S 660 .

At step S 658 , a check is performed to determine whether a next partial page has been received. If YES, program control advances to step S 626 , and if NO, it returns to step S 602 .

At step S 660 , a check is performed to determine whether the control timer times out. If the timer times out, program control goes to step S 662 , whereat an AC signal is transmitted and the retrain is executed via the control channel. Program control thereafter returns to step S 642 . When the timer does not time out, program control goes to step S 664 .

At step S 664 , a check is performed to determine whether the timer times out. If the timer does not time out, program control returns to step S 648 . If the timer times out, program control advances to step S 666 , whereat an error process is performed. Program control thereafter returns to step S 602 .

A sixth embodiment of the present invention will now be described.

As is described above, in a facsimile machine that can perform communications conforming to the ITU-T Recommendations V.8 and V.34 a retrain signal via the control channel is transmitted at a predetermined timing.

Therefore, if an AC signal (retrain) is detected, while significant data (such as a PPS-Q signal, an MCF signal and a PPR signal) for the control channel data are transmitted, the significant signals are completely destroyed, and a timer for the control channel communication times out, so that communications are disabled.

In the sixth embodiment of the present invention, provided is a facsimile machine which designates the retrain via a control channel while a partner's station is not transmitting significant data (a PPS-Q signal, an MCF signal, a PPR signal, etc.) via a control channel, whereby those significant signals can be protected from being destroyed due to the retrain, and the timer for the control channel can be prevented from timing out, so that the communications can be continued.

Since the arrangement of the facsimile machine in the sixth embodiment is the same as that in FIG. 1, an explanation will be given while referring to FIG. 1 . It should be noted that a control circuit 20 in the sixth embodiment exercises the following control.

Specifically, the control circuit 20 designates the retrain, so that, during communications conforming to the ITU-T Recommendations V.8 and V.34, the retrain via the control channel may be detected when a partner's station does not transmit significant data (e.g., PPS-Q, PPR, or an MCF signal) as control channel data.

Specifically, the retrain to be designated when a response is received after transmission of control channel date, is designated after a predetermined time (e.g., 2.2 seconds) following the initiation of the transmission of control channel data via the control channel.

For the designation of the retrain upon the receipt of a response, after transition to reception of the control channel data, the time that must elapse before designating the retrain via the control channel is changed based on a line delay. For example, assuming that a line delay for one-way is td, the retrain is designated following the elapse of the time calculated by subtracting 2td from 2.5 seconds.

FIGS. 28 to 34 are flowcharts showing the control exercised by the control circuit 20 according to the sixth embodiment.

An explanation will be given for an example where signals Sh and Sh * are used to initiate the reception of a response at the time of the transmission of a PPS-Q signal, the reception of a command after the primary transmission of data for one page have been received, and the transmission of signals.

In FIG. 28, the control circuit 20 is activated at step S 700 , and at step S 702 , it outputs a signal at level “0” across the signal line 20 a and turns off a CML. At step S 704 , the control circuit 20 outputs a signal at level “0” across the signal line 20 d to set an ANSam signal non-transmission state.

At steps S 706 and S 708 , a check is performed to determine whether reception or transmission is selected. When reception is selected, program control moves to step S 712 , and when transmission is selected, program control goes to step S 774 . When neither of them is selected, program control moves to step S 710 , whereat the other process is performed. Program control thereafter returns to step S 702 .

At step S 712 , a signal at level “1” is output across the signal line 20 a and the CML is turned on. Following this, the transmission of an ANSam signal at step S 714 , the reception of a CM signal at step S 716 , the transmission of a JM signal at step S 718 , and the reception of a CJ signal at step S 720 are sequentially performed.

At step S 722 , a line probing signal is received. At this time, a one-way delay time td for the line is considered and recorded. Then, the reception of a long training signal at step S 724 , the exchange of parameters at step S 726 , and the reception and recording of primary channel information at step S 728 are sequentially performed.

At step S 730 , a timer is set as 10 seconds for the detection of control channel data. At step S 732 , reception of signals Sh, Sh * , ALT and E, and the transmission of signals Sh, Sh * , ALT and E are performed. When the E signal has been transmitted, transmission of a flag is executed.

At step S 734 , a check is performed to determine whether or not control channel data have been detected. When control channel data have been detected, program control advances to step S 740 , and when control channel data have not been detected, program control advances to step S 736 .

At step S 736 , a check is performed to determine whether the timer times out. If the timer times out, program control advances to step S 738 , whereat an error process is performed and program control thereafter returns to step S 702 . If the timer does not time out, program control returns to step S 732 .

At step S 740 , 6 seconds are set to a timer (timer T 2 ) to receive commands, and at step S 742 , a time period (2.5 seconds−2td) is set to a timer (timer 0 ) for designating the retrain. This time period will be described later.

At step S 744 , a check is performed to determine whether a PPS-Q signal has been detected among the control channel data. If a PPS-Q signal has been detected, program control moves to step S 748 ; if not, program control advances to step S 746 . At step S 746 , a check is performed to determine whether the timer 0 times out. When the timer times out, program control moves to step S 758 , whereat the retrain is requested (this is the time during which the transmission side does not transmit a PPS-Q signal and during which the retrain process can be detected). When the timer does not time out, program control returns to step S 744 .

At step S 748 , a check is performed to determine whether there is an error in the received primary data. If there is an error, program control advances to step S 750 , whereat a PPR signal is transmitted. Program control thereafter moves to step S 728 . When there is no error, program control goes to step S 752 .

At step S 752 , a check is performed to determine whether a current page is the last page. If the current page is the last page, program control advances to step S 754 , whereat an MCF signal is transmitted. Program control thereafter moves to step S 728 . If the current page is not the last page, program control moves to step S 756 , whereat an MCF signal is transmitted and a DCN signal is received.

At step S 758 the time set for the timer T 2 is stored in a memory T 2 SAV. In other words, the timer T 2 is halted.

At step S 760 , a timing of 10 seconds is set for the timer 0 as the period that will elapse before control channel data are detected. At step S 762 , an AC signal is transmitted to request the retrain process via the control channel.

At step S 764 , the reception of signals PPh, ALT, MPh and E, and the transmission of signals PPh, ALT, MPh and E are performed. When the E signal has been transmitted, transmission of a flag is executed.

At step S 766 a check is performed to determine whether or not control channel data, which have been transmitted via the control channel from the partner's station, have been detected. When control channel data have been detected, program control advances to step S 772 , whereat the stored time T 2 SAV is used to set the timing for to the timer T 2 , and the timer T 2 begins the count down. Program control thereafter returns to step S 742 . When the control channel data have not been detected, program control advances to step S 768 .

At step S 768 , a check is performed to determine whether the time set for the timer 0 has expired. If the time has expired, program control advances to step S 770 , whereat an error process is performed. Program control thereafter returns to step S 702 . If the time has not expired, program control returns to step S 764 .

At step S 774 a signal at level “1” is output to the signal line 20 a and the CML is turned on. Following this, the reception of an ANSam signal at step S 776 , the transmission of a CM signal at step S 778 , the reception of a JM signal at step S 780 , the transmission of a CJ signal at step S 782 , the transmission of a line probing signal at step S 784 , the transmission of a long training signal at step S 786 , exchange of parameters at step S 788 , and the transmission of primary channel data at step S 790 are sequentially performed.

At step S 792 , a timing of 10 seconds is set for the timer 0 as the period that will elapse before control channel data are detected. At step S 794 , the transmission of signals Sh, Sh * , ALT and E, and the reception of signals Sh, Sh * , ALT and E are performed. When the E signal has been transmitted, transmission of a flag is executed.

At step S 796 a check is performed to determine whether or not control channel data, which have been transmitted via the control channel from the partner's station, have been detected. When control channel data have been detected, program control advances to step S 802 , and when control channel data have not been detected, program control moves to step S 798 .

At step S 798 , a check is performed to determine whether the time set for the timer 0 has expired. If the time has expired, program control advances to step S 800 , whereat an error process is performed. Program control thereafter returns to step S 702 . If the time has not expired, program control returns to step S 794 .

At step S 802 , a value of “0” is set to a PPS-Q re-transmission counter, and at step S 804 , a timing of 2.2 seconds is set for a timer (timer 0 ) for designating the retrain process. This period of time will be described later.

At step S 806 , the control circuit 20 is shifted for the processing of control channel data, and transmits a preamble signal at 100 mS. At step S 808 , a PPS-Q signal is transmitted as significant data for the control channel data, and at step S 810 , the timing for the timer T 4 is set to three seconds as the period allocated for the reception of a response.

Following this, at step S 812 , a check is performed to determine whether a significant signal can be detected among the control channel data. If a significant signal is detected, program control advances to step S 822 , and if a significant signal is not detected, program control moves to step S 814 .

At step S 814 , a check is performed to determine whether the time set for the timer 0 has expired. When the time has expired, program control moves to step S 840 , whereat the retrain process is requested (this is the time at which the reception side does not transmit signals PPR, MCF and RNR, and at which the retrain process can be detected). When the time has not expired, program control returns to step S 816 .

At step S 816 , a check is performed to determine whether the time set for the T 4 timer has expired. When the time has not expired, program control returns to step S 812 . When the time has expired, program control advances to step S 818 , whereat the count held by the re-transmission counter is incremented by one.

At step S 820 , a check is performed to determine whether a count held by the re-transmission counter is equal to three or greater. When the count is three or greater, program control advances to step S 836 , and when the count is less than three, program control returns to step S 804 .

At steps S 822 and S 824 , a check is performed to respectively determine whether a PPR signal and a MCF signal have been detected. When a PPR signal has been detected, program control returns to step S 790 , and when an MCF signal has been detected, program control advances to step S 826 . If another signal is detected, program control moves to step S 830 .

At step S 826 , a check is performed to determine whether there is a subsequent page. If there is a subsequent page, program control returns to step S 790 , and if there are no more pages, program control advances to step S 828 , whereat a DCN signal is output. Program control thereafter returns to step S 702 .

At step S 830 , a check is performed to determine whether or not an RNR signal has been detected. If an RNR signal has been detected, program control advances to step S 832 , whereat an RR signal is transmitted. Program control thereafter returns to step S 810 . If an RNR signal has not been detected, program control moves to step S 834 , whereat an error process is performed. Program control thereafter returns to step S 702 .

In addition, transmission of a DCN signal at step S 836 and an error process at step S 838 are sequentially performed, and program control thereafter returns to step S 702 .

At step S 840 , the time held by the timer T 4 is stored in a memory T 4 SAV, and the counting of the timer T 4 is halted. At step S 842 , the timing for the timer 0 is set to ten seconds as the period that will elapse before control channel data is detected. At step S 844 , an AC signal is transmitted to request the retrain process via the control channel.

At step S 846 , the reception of signals PPh, ALT, MPh and E, and the transmission of signals PPh, ALT, MPh and E are performed. When the E signal has been transmitted, transmission of a flag is executed.

At step S 848 a check is performed to determine whether or not control channel data, which have been transmitted via the control channel from the partner's station, have been detected. When control channel data have been detected, program control advances to step S 850 , whereat the stored T 4 SAV timing is set for the timer T 4 , and the counting by the timer T 4 is begun. Program control thereafter returns to step S 816 . When control channel data have not been detected, program control moves to step S 852 .

At step S 852 , a check is performed to determine whether the time set for the timer 0 has expired. If the time has expired, program control advances to step S 854 , whereat an error process is performed. Program control thereafter returns to step S 702 . If the time has not expired, program control returns to step S 846 .

FIG. 35 is a diagram of the timing for an AC signal that is to be transmitted after the shifting of the control channel data has been detected during the response transmission following the dispatching of a PPS-Q signal by a transmitter.

In this case, a retrain request must be issued only when the data shifting can not be detected at the time the PPS-Q signal has been transmitted, and then the reception of an MCF signal is terminated. Therefore, assuming that an AC signal is transmitted two seconds later than the termination of the transmission of a PPS-Q signal, 2 seconds+0.1 second (preamble time)+0.1 second (PPS-Q transmission time)=2.2 seconds is required after the shifting to the control channel data is detected, and is constant, regardless of a line delay.

FIG. 36 is a diagram showing the timing for the transmission of an AC signal when the shifting to the control channel data is detected during the command reception after the primary channel data have been received from the receiver.

In this case, an AC signal must be transmitted at a timing where by it can be detected before the transmitter transmits the next PPS-Q signal.

Assume that a first PPS-Q signal has been transmitted by the transmitter with a delay of 0 mS, and the first AC signal is received three seconds later. The transmission timing for an AC signal, after the shifting to the control channel data has been detected during the command reception, is 2.3 seconds+0.1 second (preamble time)+0.1 second (PPS-Q reception time (this signal can not be received due to an error))=2.5 seconds.

With a delay time for a one-way transmission being x mS, x mS is required by the transmitter to detect the shifting to the control channel data, and x mS is required until an AC signal is transmitted by the receiver to the transmitter, so that the transmission timing for an AC signal is (2.5 seconds−2× seconds).

Therefore, when the retrain process is executed at the above obtained timing, effective data at the control channel are not destroyed by the retrain process and communications can be continued.

In the sixth embodiment, an explanation has been given by using the response reception after the PPS-Q signal has been transmitted, and the command reception following the primary channel data have been received. This embodiment may be used, in the same manner, for response reception and command reception at another timing.

In addition, in the sixth embodiment, the transmission/reception of signals Sh, Sh * , ALT and E via the control channel have been explained; however, this embodiment can be employed for the transmission/reception of signals PPh, ALT, MPh and E.

A standalone facsimile machine has been employed for the individual embodiments, but the present invention is not limited to this type of facsimile machine, and can be employed, for example, for a host computer, a copy machine, a printer, and a system that constitutes a compound apparatus having an electronic filing function.

In addition to the above embodiments, various other modifications of the present invention can be employed.