Communication device and communication method

Abstract

To prevent a communication error from occurring even in a failure of resynchronization of a primary channel.SOLUTION: A communication apparatus with a facsimile communication function comprises: a reception unit which receives an S signal, an Sbar signal, or a PP signal, as a resynchronization signal of a primary channel; a resynchronization signal measurement unit 123 which measures a reception time in which the reception unit continues reception of the resynchronization signal of the primary channel; and a control channel shift control unit 124 which performs control to shift to a control channel in a case where the reception time is longer than a threshold time.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present disclosure relates to a communication device and a communication method. [Background technology]

[0002] 2. Description of the Related Art Facsimile communication has conventionally been carried out using a Voice over Internet Protocol (VoIP) line. For example, in a transmission procedure using a half-duplex modulation method defined in V.34 of the ITU-T (International Telecommunication Unit Telecommunication Standardization Sector) recommendation, facsimile communication is carried out in the following manner. In phase 1, the communication standard is determined, in phase 2, the symbol rate and carrier frequency are determined, and in phase 3, the equalizer training of the primary channel is performed. After phase 3, the control channel is started up, the modulation parameter sequence MPh is exchanged, and the signal rate of the primary channel is determined. After this, the primary channel resynchronization is performed.

[0003] In primary channel resynchronization, the transmitting side transmits an S signal for synchronization, an Sbar signal for synchronization, a PP signal for synchronization, sequence B1, followed by a message frame and an RCP (Rerun to Control for Partial page) frame, which indicates the end of the message.

[0004] The receiving side receives the S signal, the Sbar signal, the PP signal, and the sequence B1 in that order, thereby resynchronizing with the primary channel and being able to receive the subsequent message frame and RCP frame.

[0005] However, if the receiving side cannot receive the S signal, the Sbar signal, the PP signal, and the sequence B1, the primary channel resynchronization fails, and the message frame and the RCP frame cannot be received.

[0006] For this reason, the facsimile machine described in Patent Document 1 receives a PP signal and sequence B1 and receives a message frame and an RCP frame when the period between detection of an S signal or an Sbar signal exceeds a predetermined period. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2007-49354 A Summary of the Invention [Problem to be solved by the invention]

[0008] However, even in conventional facsimile machines, if the PP signal or sequence B1 is not detected, resynchronization of the primary channel fails, resulting in a communication error.

[0009] Therefore, one or more aspects of the present disclosure aim to prevent a communication error from occurring even if resynchronization of the primary channel fails. [Means for solving the problem]

[0010] A communication device having a facsimile communication function according to an embodiment of the present disclosure includes a receiving unit that receives an S signal, an Sbar signal, or a PP signal as a resynchronization signal on a primary channel, a resynchronization signal measuring unit that measures a reception time during which the receiving unit continues to receive the resynchronization signal on the primary channel, and a control channel transition control unit that controls a transition to a control channel when the reception time is longer than a threshold time. the threshold time is a time determined in accordance with each of the S signal, the Sbar signal, and the PP signal, and the resynchronization signal measurement unit, when the receiving unit receives the S signal, determines whether or not the reception time during which the receiving unit continues to receive the S signal is longer than the threshold time determined in accordance with the S signal, when the receiving unit receives the Sbar signal, determines whether or not the reception time during which the receiving unit continues to receive the Sbar signal is longer than the threshold time determined in accordance with the Sbar signal, and when the receiving unit receives the PP signal, determines whether or not the reception time during which the receiving unit continues to receive the PP signal is longer than the threshold time determined in accordance with the PP signal. It is characterized by:

[0011] A communication method in facsimile communication according to an embodiment of the present disclosure receives an S signal, an Sbar signal, or a PP signal as a resynchronization signal on a primary channel, measures a reception time during which the resynchronization signal on the primary channel is continuously received, and performs control to transition to a control channel when the reception time is longer than a threshold time. A communication method in facsimile communication, wherein the threshold time is a time determined in accordance with each of the S signal, the Sbar signal, and the PP signal, and when the S signal is received, it is determined whether or not the reception time during which the S signal is continuously received is longer than the threshold time determined in accordance with the S signal, when the Sbar signal is received, it is determined whether or not the reception time during which the Sbar signal is continuously received is longer than the threshold time determined in accordance with the Sbar signal, and when the PP signal is received, it is determined whether or not the reception time during which the PP signal is continuously received is longer than the threshold time determined in accordance with the PP signal. It is characterized by: Effect of the Invention

[0012] According to one or more aspects of the present disclosure, even if resynchronization of the primary channel fails, a communication error can be prevented. [Brief description of the drawings]

[0013] [Figure 1] 1 is a block diagram showing an example of a connection form in an IP line of a FAX according to an embodiment; [Diagram 2] FIG. 2 is a schematic diagram for explaining a signal sequence for half-duplex operation defined in ITU-T Recommendation V.34. [Diagram 3] This is the signal sequence when there is a continuing facsimile document. [Figure 4] 4 is a signal sequence when there are no continuing facsimile documents. [Diagram 5] FIG. 1 is a block diagram showing a schematic configuration of a FAX according to an embodiment. [Figure 6] FIG. 2 is a block diagram illustrating a schematic configuration of a control unit. [Figure 7] 1A and 1B are block diagrams illustrating an example of a hardware configuration. [Figure 8] 13 is a flowchart showing a primary channel resynchronization process of a FAX. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] FIG. 1 is a block diagram showing an example of a connection state of facsimile machines (hereinafter, referred to as FAX) 110A and 110B according to an embodiment of the present invention on an IP (Internet Protocol) line. The facsimile communication system 100 shown in FIG. 1 includes FAX devices 110A and 110B, VoIP terminal adaptors (TAs) 101A and 101B, and routers 102A and 102B. The routers 102A and 102B are connected to an IP line 103.

[0015] Here, since the FAXes 110A and 110B have the same configuration, when there is no need to particularly distinguish between the FAXes 110A and 110B, each of the FAXes 110A and 110B will be referred to as FAX 110.

[0016] Here, facsimile communication in which image information is transmitted from FAX 110A as a transmitter to FAX 110B as a receiver via IP line 103 will be described. In facsimile communication via the IP line 103, a facsimile transmission signal is regarded as a voice signal, and the voice signal is processed into voice packets for communication by VoIP.

[0017] FAX 110A is connected to VoIP-TA 101A and transmits a facsimile signal as an analog voice signal. The VoIP-TA 101A generates encoded voice information by encoding this facsimile signal in accordance with ITU-T Recommendation G.711, and sends the encoded voice information to the router 102A.

[0018] The router 102A is connected to the VoIP-TA 101A and the IP line 103, and receives voice information encoded by the VoIP-TA 101A. The router 102A generates RTP packets by packetizing the encoded audio information according to the Real-time Transport Protocol (RTP). For example, the router 102A generates RTP packets by storing encoded audio information of a predetermined packet size (e.g., 20 msec). The router 102A then transmits an RTP frame, which is made up of successive RTP packets, to the IP line 103. Router 102A connects to and disconnects from IP line 103 in accordance with instructions from VoIP-TA 101A, and selects a route to destination router 102B to enable communication.

[0019] The IP line 103 is a telephone line via the Internet, and transmits RTP packets to any destination.

[0020] The router 102B is connected to the IP line 103 and the VoIP-TA 101B, receives RTP packets from the IP line 103, extracts encoded voice information from the RTP packets, and sends the encoded voice information to the VoIP-TA 101B.

[0021] The VoIP-TA 101B is connected to the router 102B and the FAX 110B, and generates a facsimile signal by decoding the encoded voice information based on the ITU-T Recommendation G.711.Then, the VoIP-TA 101B transmits the facsimile signal to the FAX 110B. FAX 110B receives a facsimile signal and records it on a recording paper medium (not shown).

[0022] In facsimile communication, the transmitter and receiver generally synchronize with each other while repeatedly transferring procedure signals and image data. In this manner, in a communication method that requires synchronization between the transmitter and receiver, the loss of a communication signal will cause the transmitter and receiver to lose synchronization.

[0023] In addition, ITU-T Recommendation T.30 Annex F specifies the transmission procedures using the half-duplex modulation method specified in ITU-T Recommendation V.34, and requires the use of the error correction mode (ECM) specified in ITU-T Recommendation T.4 Annex A.

[0024] In the error correction mode, the transmitting facsimile machine divides image information to be transmitted by facsimile communication into a plurality of message frames to which information capable of detecting errors is added, and then transmits the message frames. When the receiving facsimile machine detects an error in the received message frame, it requests the transmitting facsimile machine to resend the erroneous frame. When the transmitting facsimile device receives a resend request from the receiving facsimile device, it resends the frame for which the resend request was made to the receiving facsimile device.

[0025] 2 to 4 are schematic diagrams for explaining signal sequences for half-duplex operation as defined in ITU-T Recommendation V.34. As shown in Figure 2, in half-duplex operation as defined in ITU-T Recommendation V.34, the communication standard is determined in phase 1, the symbol rate and carrier frequency are determined in phase 2, and equalizer training of the primary channel is performed in phase 3.

[0026] After phase 3, control channel synchronization is performed and the modulation parameter sequence MPh is exchanged to determine the signal rate of the primary channel. Then, primary channel resynchronization occurs.

[0027] In primary channel resynchronization, the transmitting facsimile machine transmits a 128-symbol S signal for synchronization, a 16-symbol Sbar signal for synchronization, a 288-symbol PP signal for synchronization, and sequence B1, followed by a message frame and an RCP frame indicating the end of the message.

[0028] In primary channel resynchronization, the receiving facsimile machine roughly synchronizes its clock with the modem of the sending facsimile machine by detecting the S signal and the transition from the S signal to the Sbar signal. The receiving facsimile machine then performs synchronization using the subsequent PP signal, and then receives signals up to the message frame and RCP frame.

[0029] Thereafter, the control channel resynchronization shown in FIG. 3 or FIG. 4 is performed, followed by a post-message procedure including a procedure for retransmitting the erroneous frame on the control channel. FIG. 3 shows the signal sequence when there is a subsequent facsimile document, and FIG. 4 shows the signal sequence when there is no subsequent facsimile document.

[0030] If the receiving facsimile machine receives the message frame correctly, it returns MCF in the post-message procedure. On the other hand, if there is an error in the message frame, the receiving facsimile machine can request a retransmission of the message frame that it could not receive by returning PPR.

[0031] When the sending facsimile machine receives a PPR in the post-message procedure, it resends only the erroneous portion. On the other hand, when it receives an MCF, the sending facsimile machine sends the next page if there is one, and if there is not, it sends a DCN and performs disconnection processing.

[0032] By repeating the transmission of the message frame on the primary channel and the transmission in the post-message procedure on the control channel, facsimile communication using the error correction mode is realized.

[0033] In primary channel resynchronization, the receiving facsimile machine must receive the S signal, Sbar signal, and PP signal correctly in that order. If the receiving facsimile machine cannot receive the S signal, Sbar signal, and PP signal correctly in that order, the sequence will not proceed. On the other hand, when the transmitting facsimile machine finishes transmitting the primary channel, it moves to the control channel resynchronization procedure as shown in Figure 3 or Figure 4. Here, the transmitting facsimile machine transmits the Sh signal, the Shbar signal, and the sequence ALT, and waits for the Sh signal or the PPh signal from the receiving modem.

[0034] Furthermore, some receiving device of a VoIP line, for example, a VoIP-TA, may have a PLC (Packet Loss Concealment) function. The PLC function is a function that fills in the lost voice part by interpolating the lost part using the voice data before and after the packet loss in order to prevent the voice cut-out from causing discomfort in the conversation, making the voice conversation less awkward.

[0035] However, this PLC function inserts false facsimile signals in facsimile communications, which can cause communication errors. Thus, if packet loss occurs during primary channel resynchronization and the PLC function performs interpolation of the voice data, neither the sending nor the receiving facsimile machine can proceed, resulting in a failure of the facsimile communication.

[0036] FIG. 5 is a block diagram showing a schematic configuration of FAX 110 according to the embodiment. The FAX 110 includes a storage unit 111 , a reading unit 112 , a printing unit 113 , an operation unit 114 , a communication unit 115 , and a control unit 120 .

[0037] The storage unit 111 is a storage device that uses a ROM (Read Only Memory) or a RAM (Random Access Memory), etc. For example, the storage unit 111 stores a program, which is software executed by the control unit 120. The storage unit 111 also stores data generated when the program is executed and data used when the program is executed.

[0038] For example, the storage unit 111 functions as a resynchronization signal time storage unit that stores predetermined values ​​as the durations of the S signal, the Sbar signal, and the PP signal, which are resynchronization signals of the primary channel defined in ITU-T Recommendation V.34.The durations are threshold times for comparison with the reception times during which the respective signals are received. The duration of each signal may be determined so that the faster the symbol rate determined in phase 2 of the V.34 communication sequence shown in Fig. 2, the shorter the duration. Specifically, the duration of each signal may be determined by dividing the number of symbols of each resynchronization signal (e.g., S signal: 128T, Sbar signal: 16T, PP signal: 288T) specified in ITU-T Recommendation V.34 by its symbol rate (e.g., 2400, 2800, 3000, 3200, or 3429 [symbols / second]), or by a value that increases as the divided value increases. In other words, the duration may be determined by dividing the number of symbols of each resynchronization signal by the slowest symbol rate.

[0039] The value calculated as above may take into consideration a predetermined detection error. For example, the larger the predetermined detection error, the larger the adjustment value may be added to the calculated value. Specifically, if the timer that measures the duration has a measurement error of ±10%, the adjustment value may be 10% of the value calculated as above. The adjustment value may be changed by the user via the operation unit 114.

[0040] The reading unit 112 is a scanner device that uses a CCD (Charge Coupled Device) or the like (not shown). The reading unit 112 reads an image from a document and converts it into dot image data. The dot image data is encoded in accordance with ITU-T Recommendation T.4 or the like. The encoded data is stored in the memory unit 111.

[0041] The printing unit 113 is a printer device (not shown) of a thermal recording type or an electrophotographic type, etc. The printing unit 113 decodes the image data received by the communication unit 115 in accordance with ITU-T Recommendation T.4 or the like, and outputs it as a hard copy.

[0042] The operation unit 114 includes a display unit that displays the status of the FAX 110 using a display device such as an LCD (Liquid Crystal Display), and an input unit such as a numeric keypad or start key for setting various setting values ​​required to operate the FAX 110.

[0043] The communication unit 115 is a communication device that performs communication and is made up of an NCU (Network Control Unit) that controls the connection with the telephone line 104, a modem 116, and the like.

[0044] The modem 116 modulates digital signals into analog signals that match the characteristics of the transmission line and transmits them, and also demodulates analog signals from the transmission line into digital signals and receives them. Image data and procedure signals exchanged between the FAX machines 110 are sent and received via this modem 116. In other words, the modem 116 functions as a receiving unit that receives an S signal, an Sbar signal, or a PP signal as a resynchronization signal of the primary channel.

[0045] The control unit 120 controls the processing in the FAX 110. For example, the control unit 120 controls the storage unit 111, the reading unit 112, the printing unit 113, the operation unit 114, and the communication unit 115 via the system bus 117.

[0046] FIG. 6 is a block diagram showing a schematic configuration of control unit 120. As shown in FIG. The control unit 120 includes a reception control unit 121, a resynchronization signal processing unit 122, a resynchronization signal measuring unit 123, and a control channel transition control unit .

[0047] The reception control unit 121 controls the execution of facsimile reception. For example, the reception control unit 121 controls the resynchronization signal processing unit 122, the resynchronization signal measuring unit 123, and the control channel transition control unit 124 when executing facsimile reception.

[0048] The resynchronization signal processing unit 122 monitors whether or not the modem 116 included in the communication unit 115 has detected each of the S signal, the Sbar signal, the PP signal, and the sequence B1, which are resynchronization signals of the primary channel.

[0049] When the resynchronization signal processing unit 122 detects each resynchronization signal of the primary channel, the resynchronization signal measurement unit 123 starts measurement and determines whether the duration of the corresponding signal stored in the memory unit 111 has expired. For example, the resynchronization signal measuring unit 123 measures the reception time during which the communication unit 115 continues to receive the resynchronization signal on the primary channel. Then, the resynchronization signal measuring unit 123 determines whether the reception time is longer than the duration.

[0050] Specifically, when the communication unit 115 receives an S signal, the resynchronization signal measurement unit 123 determines whether the reception time during which the communication unit 115 continues to receive the S signal is longer than the threshold time duration determined according to the S signal. Also, when the communication unit 115 receives an Sbar signal, the resynchronization signal measurement unit 123 determines whether the reception time during which the communication unit 115 continues to receive the Sbar signal is longer than the threshold time duration determined according to the Sbar signal. Furthermore, when the communication unit 115 receives a PP signal, the resynchronization signal measurement unit 123 determines whether the reception time during which the communication unit 115 continues to receive the PP signal is longer than the threshold time duration determined according to the PP signal.

[0051] The control channel transition control unit 124 performs control to transition to the control channel when the reception time of the resynchronization signal on the primary channel is longer than a threshold time. For example, when the reception time is longer than a duration that is a threshold time, the control channel transition control unit 124 causes the communication unit 115 to stop receiving the resynchronization signal on the primary channel and to receive the resynchronization signal on the control channel. Specifically, the control channel transition control unit 124 controls the modem 116 included in the communication unit 115 to stop receiving the primary channel and transition to waiting for a resynchronization signal on the control channel.

[0052] A part or the whole of the control unit 120 described above can be configured, for example, as shown in Fig. 7(A), by a memory 10 and a processor 11 such as a CPU (Central Processing Unit) that executes a program stored in the memory 10. Such a program may be provided through a network, or may be provided by being recorded on a recording medium. That is, such a program may be provided, for example, as a program product. The memory 10 may be a storage unit 111 shown in FIG.

[0053] In addition, a part or all of the control unit 120 may be configured with a processing circuit 12 such as a single circuit, a composite circuit, a processor operated by a program, a parallel processor operated by a program, an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array), for example, as shown in FIG. 7(B). As described above, the control unit 120 can be realized by a processing circuit network.

[0054] FIG. 8 is a flowchart showing the primary channel resynchronization process of the FAX 110. First, the resynchronization signal processor 122 determines whether or not the modem 116 has detected an S signal, which is a resynchronization signal of ITU-T Recommendation V.34 (S10). If an S signal has been detected (Yes in S10), the process proceeds to step S11.

[0055] In step S11, the resynchronization signal measurement unit 123 starts measuring the duration of the S signal, which is a resynchronization signal on the primary channel.

[0056] Next, resynchronization signal measuring unit 123 starts measurement in step S11, and determines (S12) whether the reception time, which is the time during which modem 116 continues to receive the S signal, has become longer than the duration of the S signal stored in storage unit 111. If the reception time has become longer than the duration of the S signal (Yes in S12), the process proceeds to step S20, and if the reception time is equal to or shorter than the duration of the S signal (No in S12), the process proceeds to step S13.

[0057] In step S13, the resynchronization signal processor 122 determines whether or not the modem 116 has detected an Sbar signal, which is a resynchronization signal of ITU-T Recommendation V.34. If an Sbar signal is detected (Yes in S13), the process proceeds to step S14, and if an Sbar signal is not detected (No in S13), the process returns to step S12.

[0058] In step S14, the resynchronization signal measuring unit 123 starts measuring the duration of the Sbar signal, which is the resynchronization signal on the primary channel.

[0059] Next, the resynchronization signal measuring unit 123 starts measurement in step S14, and determines (S15) whether the reception time, which is the time during which the modem 116 continues to receive the Sbar signal, has become longer than the duration of the Sbar signal stored in the storage unit 111. If the reception time has become longer than the duration of the Sbar signal (Yes in S15), the process proceeds to step S20, and if the reception time is equal to or shorter than the duration of the Sbar signal (No in S15), the process proceeds to step S16.

[0060] In step S16, the resynchronization signal processor 122 determines whether or not the modem 116 has detected a PP signal, which is a resynchronization signal of ITU-T Recommendation V.34. If a PP signal is detected (Yes in S16), the process proceeds to step S17, and if a PP signal is not detected (No in S16), the process returns to step S15.

[0061] In step S17, the resynchronization signal measurement unit 123 starts measuring the duration of the PP signal, which is the resynchronization signal on the primary channel.

[0062] Next, resynchronization signal measuring unit 123 starts measurement in step S17, and determines (S18) whether the reception time, which is the time during which modem 116 continues to receive the PP signal, has become longer than the duration of the PP signal stored in storage unit 111. If the reception time has become longer than the duration of the PP signal (Yes in S18), the process proceeds to step S20, and if the reception time is equal to or shorter than the duration of the PP signal (No in S18), the process proceeds to step S19.

[0063] In step S19, resynchronization signal processor 122 determines whether modem 116 has detected sequence B1 of ITU-T Recommendation V.34. If sequence B1 is detected (Yes in S19), reception controller 121 causes modem 116 to transition to primary channel data reception processing. If sequence B1 is not detected (No in S19), the process returns to step S18.

[0064] In step S20, the control channel transition control unit 124 controls transition to the control channel. Specifically, the control channel transition control unit 124 controls the modem 116 included in the communication unit 115 to forcibly stop the receiving process of the primary channel and transition to a state of waiting for detection of a resynchronization signal on the control channel. This allows the modem 116 to detect the resynchronization signal on the control channel.

[0065] In the embodiment described above, the resynchronization signal processing unit 122 monitors whether or not the modem 116 has detected each of the resynchronization signals, that is, the S signal, the Sbar signal, and the PP signal, but the embodiment is not limited to such an example. For example, depending on an interface with the modem 116 included in the communication unit 115, the detection of each signal of the resynchronization signal may not be notified, so the resynchronization signal processing unit 122 may monitor the duration of the signal reception state of the modem 116. Specifically, the resynchronization signal processing unit 122 may monitor whether or not the reception time as the time during which the modem 116 is in each reception state, such as receiving an S signal or an Sbar signal, receiving a PP signal, or receiving primary channel data, becomes longer than the duration specified for each reception state.

[0066] In other words, in this case, the duration that is the threshold time is a time that is predetermined according to the pair of the S signal and the Sbar signal, or a time that is determined according to the PP signal. When the communication unit 115 receives the pair of the S signal and the Sbar signal, the resynchronization signal measurement unit 123 determines whether or not the reception time during which the communication unit 115 continues to receive the pair of the S signal and the Sbar signal is longer than the duration that is the threshold time that is determined according to the pair of the S signal and the Sbar signal. When the communication unit 115 receives the PP signal, the resynchronization signal measurement unit 123 determines whether or not the reception time during which the communication unit 115 continues to receive the PP signal is longer than the duration that is the threshold time that is determined according to the PP signal.

[0067] According to the above embodiment, the FAX 110 measures the reception time of each resynchronization signal, which is an S signal, an Sbar signal, or a PP signal transmitted from the transmitting side when resynchronizing the primary channel. Furthermore, the reception time is compared with a duration predefined for each resynchronization signal, and if the reception time is longer than the corresponding duration, control is performed to transition to the control channel. As a result, even if a voice packet including a resynchronization signal for receiving data in the primary channel is lost and the PLC function is used to perform an interpolation process for the voice data and the primary channel fails to be resynchronized, error correction can be performed in the error correction mode defined in ITU-T Recommendation T.4 Annex A.

[0068] Although the embodiment described above has been explained using the FAX 110 as an example, the present embodiment is not limited to such an example. For example, the present embodiment can be applied to any communication device, such as a multifunction device, that has a facsimile communication function. [Explanation of symbols]

[0069] 110 FAX, 111 memory unit, 112 reading unit, 113 printing unit, 114 operation unit, 115 communication unit, 116 modem, 120 control unit, 121 reception control unit, 122 resynchronization signal processing unit, 123 resynchronization signal measurement unit, 124 control channel transition control unit.

Claims

1. a receiving unit for receiving an S signal, an Sbar signal, or a PP signal as a resynchronization signal for a primary channel; a resynchronization signal measurement unit that measures a reception time during which the receiving unit continues to receive a resynchronization signal on the primary channel; a control channel transition control unit that performs control to transition to a control channel when the reception time is longer than a threshold time, the threshold time is a time determined in accordance with each of the S signal, the Sbar signal, and the PP signal, When the receiving unit receives the S signal, the resynchronization signal measurement unit determines whether or not the reception time during which the receiving unit continues to receive the S signal is longer than the threshold time determined in accordance with the S signal, when the receiving unit receives the Sbar signal, the resynchronization signal measurement unit determines whether or not the reception time during which the receiving unit continues to receive the Sbar signal is longer than the threshold time determined in accordance with the Sbar signal, and when the receiving unit receives the PP signal, the resynchronization signal measurement unit determines whether or not the reception time during which the receiving unit continues to receive the PP signal is longer than the threshold time determined in accordance with the PP signal. A communication device having a facsimile communication function,

2. a receiving unit for receiving an S signal, an Sbar signal, or a PP signal as a resynchronization signal for a primary channel; a resynchronization signal measurement unit that measures a reception time during which the receiving unit continues to receive a resynchronization signal on the primary channel; a control channel transition control unit that performs control to transition to a control channel when the reception time is longer than a threshold time, the threshold time is a time that is predetermined according to a pair of the S signal and the Sbar signal, or a time that is predetermined according to the PP signal, When the receiving unit receives the pair of the S signal and the Sbar signal, the resynchronization signal measurement unit determines whether or not the reception time during which the receiving unit continues to receive the pair of the S signal and the Sbar signal is longer than the threshold time determined according to the pair of the S signal and the Sbar signal, and when the receiving unit receives the PP signal, the resynchronization signal measurement unit determines whether or not the reception time during which the receiving unit continues to receive the PP signal is longer than the threshold time determined according to the PP signal. A communication device having a facsimile communication function,

3. When the reception time is longer than the threshold time, the control channel transition control unit causes the receiving unit to stop receiving a resynchronization signal on the primary channel and to receive a resynchronization signal on the control channel.

3. The communication device according to claim 1 or 2.

4. The threshold time is shorter as the symbol rate defined in ITU-T Recommendation V.34 is faster. A communication device according to any one of claims 1 to 3.

5. receiving an S signal, an Sbar signal, or a PP signal as a resynchronization signal for a primary channel; Measure a reception time during which the resynchronization signal of the primary channel is continuously received; A communication method for facsimile communication that performs control to transition to a control channel when the reception time is longer than a threshold time, comprising: the threshold time is a time determined in accordance with each of the S signal, the Sbar signal, and the PP signal, When the S signal is received, it is determined whether or not the reception time during which the S signal is continuously received is longer than the threshold time determined in response to the S signal; when the Sbar signal is received, it is determined whether or not the reception time during which the Sbar signal is continuously received is longer than the threshold time determined in response to the Sbar signal; and when the PP signal is received, it is determined whether or not the reception time during which the PP signal is continuously received is longer than the threshold time determined in response to the PP signal. A communication method for facsimile communication, comprising:

6. receiving an S signal, an Sbar signal, or a PP signal as a resynchronization signal for a primary channel; Measure a reception time during which the resynchronization signal of the primary channel is continuously received; A communication method for facsimile communication that performs control to transition to a control channel when the reception time is longer than a threshold time, comprising: the threshold time is a time that is predetermined according to a pair of the S signal and the Sbar signal, or a time that is predetermined according to the PP signal, When the pair of the S signal and the Sbar signal is received, it is determined whether or not the reception time during which the pair of the S signal and the Sbar signal is continued is longer than the threshold time determined according to the pair of the S signal and the Sbar signal, and when the PP signal is received, it is determined whether or not the reception time during which the reception of the PP signal is continued is longer than the threshold time determined according to the PP signal. A communication method for facsimile communication, comprising:

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