Abstract:
The present invention is intended to attenuate a ringer tone signal, during a state in which a call is in progress, below the ringer tone signal level that occurs during a state in which no call is in progress, when a PC terminal is utilized as a telephone. A voice call system includes a handset unit for making a call, and a hook switch detection unit for detecting an on-hook/off-hook state of the handset unit. The PC terminal includes a sound source interface unit connected to a sound source, a fixed storage device for storing setting data indicative of a sound source for making a voice call, and a communication control unit responsive to a ringer tone generating operation command issued by the voice exchanger for determining whether or not a call is in progress from an on-hook/off-hook state detected by the hook switch detection unit.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a voice call system for making a call between terminals, and more particularly, to a voice call system which employs a personal computer terminal (hereinafter called the “PC terminal”).  
         [0003]     2. Description of the Related Art  
         [0004]     The following voice call systems are enumerated as proposing new ideas in transmission of a ringer tone to a receiving terminal during a telephone conversation.  
         [0005]     JP-A-58-62956 and JP-A-10-108256 disclose that a ringer tone signal is attenuated in a calling state to a level lower than that in a non-calling state.  
         [0006]     The foregoing JP-A-58-62956 relates to a push button telephone, while JP-A-10-108256 relates to a portable telephone. Additionally, in recent years, many voice call systems utilize PC terminals as telephones.  
         [0007]     In a voice call system which utilizes PC terminals as telephones, a ringer tone required by the voice call system, and sound used by an operating system (OS) or by other applications (hereinafter abbreviated as “OS system sound”) are generated by using a sound source equipped in the PC terminals.  
         [0008]     For the voice call system which utilizes PC terminals as telephones, it is also desirable to attenuate a ringer tone signal during a calling state to a level lower than that during a non-calling state, however, a PC terminal may be connected with one or a plurality of sound sources, and they can be frequently plugged into and unplugged from the PC terminal through external terminals such as USB terminals. This makes it difficult to identify from which sound source a ringer tone or OS system sound is generated, so that conventional software which implements a voice call on a PC terminal cannot decrease the volume, or turn off the volume only when such sound is generated from a sound source which is being used in a call. While it is contemplated that such control is conducted from an exchanger, uniform control from the exchanger is difficult because it cannot correctly keep track of situations in which the sound sources are placed in the PC terminal in real time, thus giving rise to the problem in which a ringer tone that is generated from a speaker, associated with a sound source that is being used for the call will interfere with the call, or that, on the contrary, no ringer tone is generated even when there is an incoming call during a conversation, so that the called party is not aware of the incoming call.  
         [0009]     Also, when a sound source is shared by OS system sound, voice call, and ringer tone due to a PC terminal having only one sound source, or the like, the OS system sound generated during a conversation may interfere with the conversation. In this even, the volume of OS sound can be set only by the sound source in many cases, so that if there is only one sound source available, it is difficult to decrease only the OS system sound. Also, since the absence of the OS system sound is inconvenient when a call is in progress, the foregoing problem cannot be solved by setting the volume of the OS system sound.  
       SUMMARY OF THE INVENTION  
       [0010]     The present invention has been made in view of the problems experienced by the prior art as described above, and it is an object of the present invention to automatically determine, upon generation of a ringer tone whether, except for a sound source, there is a ringer tone source for calling, to avoid generating ring tone, or to generate a ringer tone after its volume has been decreased during a conversation when there is no sound source dedicated to the ringer tone, to generate the ringer tone during a conversation from a separate ringer tone source, if any, to restrain OS system sound or decrease only the volume thereof during a conversation, and to generate the OS system sound at a normal volume when no call is in progress, thereby accomplishing attenuation of the ringer tone signal during a calling state to a level lower than that of the ringer tone signal during a non-calling state even in a voice call system which utilizes a PC terminal as a telephone.  
         [0011]     A voice call system according to the present invention having a PC terminal and a voice exchanger connected through a voice communications network and a voice call line, for making a voice call through the PC terminal which is controlled by the voice exchanger for reception, origination, and voice communication.  
         [0012]     The system comprises:  
         [0013]     a handset unit for making a call; and  
         [0014]     a hook switch detection unit for detecting an on-hook/off-hook of the handset unit,  
         [0015]     wherein the PC terminal comprises:  
         [0016]     a sound source interface unit connected to a sound source;  
         [0017]     a fixed storage device for storing setting data indicative of a sound source for use in making a voice call; and  
         [0018]     a communication control unit responsive to a ringer tone generating operation command issued by the voice exchanger for determining whether or not a call is in progress based on the on-hook/off-hook state detected by the hook switch detection unit, for determining from contents stored in the fixed storage device whether or not a sound source for a ringer tone generating operation is the same as a call sound source, and for decreasing the volume of a ringer tone or muting the ringer tone when a call is in progress and when the sound source for the ringer tone generating operation is the same as the call sound source.  
         [0019]     A voice call system according to another aspect of the present invention having a PC terminal and a voice exchanger connected through a voice communications network and a voice call line, for making a voice call through the PC terminal which is controlled by the voice exchanger for reception, origination, and voice communication. The system comprises:  
         [0020]     a handset unit for making a call;  
         [0021]     a base unit for the handset unit; and  
         [0022]     a sound input/output switching unit for connecting sound data transmitted/received to/from a PC interface unit that is connected to the PC terminal to the handset unit or to the base unit in accordance with an on-hook/off-hook state of the handset unit,  
         [0023]     wherein the PC terminal comprises:  
         [0024]     a sound source interface unit connected to a sound source;  
         [0025]     a fixed storage device for storing setting data indicative of a sound source that is used for in making a voice call; and  
         [0026]     a communication control unit responsive to a ringer tone generating operation command issued by the voice exchanger for determining whether or not a call is in progress based on to which the sound input/output switching unit is connected, for determining based on contents stored in the fixed storage device whether a sound source for a ringer tone generating operation is the same as a call sound source, and for decreasing the volume of a ringer tone or muting the ringer tone when the sound source for the ringer tone generating operation is the same as the call sound source.  
         [0027]     A voice call system according to a further aspect of the present invention has a PC terminal and a voice exchanger connected through a voice communications network and a voice call line, for making a voice call through the PC terminal which is controlled by the voice exchanger for reception, origination, and voice communication. The PC terminal comprises:  
         [0028]     a sound source interface unit connected to a sound source;  
         [0029]     a fixed storage device for storing a state during which a call is in progress, notified from the voice exchanger, and setting data indicative of a sound source for use in making a voice call; and  
         [0030]     a communication control unit responsive to a ringer tone generating operation command issued by the voice exchanger for determining from contents stored in the fixed storage device whether or not a call is in progress, and whether or not a sound source for a ringer tone generating operation is the same as a call sound source, and for decreasing the volume of a ringer tone or muting the ringer tone when a call is in progress and when the sound source for the ringer tone generating operation is the same as the call sound source.  
         [0031]     A voice call system according to yet a further aspect of the present invention having a PC terminal and a voice exchanger connected through a voice communications network and a voice call line, for making a voice call through the PC terminal which is controlled by the voice exchanger for reception, origination, and voice communication. The PC terminal comprises:  
         [0032]     a voice data processing unit for transmitting/receiving voice data when a voice call is made;  
         [0033]     a sound source interface unit connected to a sound source;  
         [0034]     a fixed storage device for storing a state during which a call is in progress, notified from the voice exchanger and setting data indicative of a sound source for use in making a voice call; and  
         [0035]     a communication control unit responsive to a ringer tone generating operation command issued by the voice exchanger for determining whether or not a call is in progress based on whether or not the voice data processing unit is transmitting/receiving voice data, and for determining whether or not a sound source for a ringer tone generating operation is the same as a call sound source, and for decreasing the volume of a ringer tone or muting the ringer tone when a call is in progress and when the sound source for ringer-tone generating operation is the same as the call sound source.  
         [0036]     In any of the voice call systems described above, the communication control unit decreases the volume of, or mutes sound associated with an operating system of the PC terminal and sound associated with another application.  
         [0037]     In the present invention, it is automatically determined whether a ringer tone source is provided, in addition to a call sound, source when a ringer tone is generated, and the ringer tone is muted or emitted with a decreased volume during a conversation when no ringer tone source is provided. When a separate ringer tone source is provided, the ringer tone is emitted from this sound source during a conversation.  
         [0038]     In the present invention, OS system sound is restrained or decreased in volume during a conversation. When no call is in progress, the OS system sound is generated at a normal volume.  
         [0039]     As described above, the present invention attenuates a ringer tone signal, during a state when a call is made, below the level of the ringer tone signal during a state when a call is made, even in a voice communication system which utilizes a PC terminal as a telephone. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0040]      FIG. 1  is a block diagram generally illustrating the configuration of one embodiment of the present invention;  
         [0041]      FIG. 2  is a block diagram illustrating the configuration of PC terminal  102  in  FIG. 1 ;  
         [0042]      FIG. 3  is a diagram illustrating the configuration of software modules stored in memory  205  within PC terminal  102 ;  
         [0043]      FIG. 4  is a block diagram illustrating the configuration of handset sound source  207  connected to PC terminal  102 ;  
         [0044]      FIG. 5  is a diagram showing contents in a setting data storage area for voice call application  301 , stored in fixed storage device  209  of PC terminal  102 ;  
         [0045]      FIG. 6  is a flow chart illustrating the operation of the embodiment illustrated in  FIG. 1 ;  
         [0046]      FIG. 7  is a flow chart illustrating the operation of the embodiment illustrated in  FIG. 1 ;  
         [0047]      FIG. 8  is a flow chart illustrating the operation according to a third embodiment of the present invention;  
         [0048]      FIG. 9  is a flow chart illustrating the operation according to a fourth embodiment of the present invention;  
         [0049]      FIG. 10  is a flow chart illustrating the operation according to a fifth embodiment of the present invention;  
         [0050]      FIG. 11  is a flow chart illustrating the operation according to a sixth embodiment of the present invention;  
         [0051]      FIG. 12  is a flow chart illustrating the operation according to a seventh embodiment of the present invention;  
         [0052]      FIG. 13  is a flow chart illustrating the operation according to an eighth embodiment of the present invention; and  
         [0053]      FIG. 14  is a flow chart illustrating the operation according to a ninth embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0054]     Next, embodiments of the present invention will be described with reference to the drawings.  
         [0055]      FIG. 1  is a block diagram generally illustrating the configuration according to one embodiment of the present invention, showing the configuration of office/home  105  connected to voice communications network  104 .  
         [0056]     Office/home  105  is equipped with voice exchanger  101  for exchanging voice communications; PC terminal  102  installed on a desk of an operator; and gate way  103  arranged between voice exchanger  101  and PC terminal  102  and voice communications network  104 , where these components are interconnected through voice call line  106 .  
         [0057]     Voice exchanger  101  communicates with voice communications network  104  to control reception, origination, and voice communication between PC terminal  102  and voice communications network  104 .  
         [0058]      FIG. 2  is a block diagram illustrating the configuration of PC terminal  102 . Referring to  FIG. 2 , a description will be given of the configuration and operation of PC terminal  102 .  
         [0059]     PC terminal  102  comprises user I/F (interface) unit  201 ; sound source I/F unit  202 , voice line I/F unit  203 ; CPU  204 ; memory  205 ; and fixed storage device  209 .  
         [0060]     User I/F unit  201  receives input signals from a mouse, a keyboard, and display  206  connected to PC terminal  102 , and supplies a video signal to display  206 . Sound source I/F unit  202  transmits/receives voice data to/from handset sound source  207  and a plurality of sound sources  209  connected to PC terminal  102 . Voice line I/F unit  203  transmits/receives signals to/from voice call line  106 . CPU  204  controls overall PC terminal  102 . Memory  205  is used as a work area for using software and data required to control PC terminal  102 . Fixed storage device  209  stores software and data.  
         [0061]      FIG. 3  is a diagram illustrating the configuration of software modules implemented in memory  205  within PC terminal  102 . The software modules of this embodiment comprise voice call application  301 , sound source using application  309 , and OS  310 .  
         [0062]     Voice call application  301 , which is application software running on OS  310  for making voice calls, comprises ringer tone file reading unit  302 , ringer tone generation unit  303 , ringer tone volume control unit  304 , voice data processing unit  305 , volume control unit  306 , sound source input/output unit  307 , voice line input/output unit  308 , and communication control unit  320 .  
         [0063]     OS  301  comprises fixed storage device storage unit  314 , voice line I/F control unit  315 , OS system sound output control unit  311 , sound source control I/F&#39;s, sound source volume control units, and sound source control units, and is installed in PC terminal  102 . One set of the sound source control I/F, sound source volume control unit, and sound source control unit is provided for each sound source, and these components numbered in  FIG. 3  include sound source control I/F  312 , sound source volume control unit  316 , and sound source control unit  318  provided for sound source  1 , and sound source control I/F  313 , sound source volume control unit  317 , and sound source control unit  319  provided for sound source  2 , but the number of these sets is as large as the number of sound sources.  
         [0064]     Each of the foregoing modules and the respective components which form part of each of the modules are implemented in memory  205  by programs supplied from the outside, and cooperate with CPU  204  to perform a variety of control operations and processing operations. The programs may be installed in memory  205  from a storage medium such as CD-ROM, floppy disk, external memory device or the like through an interface, or may be delivered through a network, for example, the Internet.  
         [0065]     Ringer tone file reading unit  302  reads a ringer tone waveform data file from fixed storage unit  209  through OS  310 , ringer tone generation unit  303  converts the format of the read ringer tone waveform data such that it can be reproduced on OS  310 , and ringer tone volume control unit  304  increases or decreases the volume of the converted ringer tone data based on a previously set value.  
         [0066]     Voice data processing unit  305  receives voice communication data acquired by voice line input/output unit  308  from a voice line through OS  310 , converts the format of the voice communication data such that it can be reproduced on OS  310 , and passes the converted data to volume control unit  306 . Voice data processing unit  305  also receives, through volume control unit  306 , voice input waveform data from a sound source received by sound source input/output unit  307  through OS  310 , and passes the data to voice line input/output unit  308 .  
         [0067]     Volume control unit  306  increases or decreases the volume of sound waveform data received from ringer tone volume control unit  304  and voice data processing unit  305 , based on a previously set value, and passes the resulting sound waveform data to sound source input/output unit  307 . Volume control unit  306  also receives a voice input waveform, from a sound source from sound source input/output unit  307  through OS  310 , increases or decreases the volume of the voice input waveform based on a previously set value, and passes the resulting data to voice data processing unit  305 .  
         [0068]     Sound source input/output unit  307  receives the microphone input waveform of a sound source from the sound source control I/F of OS  310 , and passes the microphone input waveform to volume control unit  306 . Sound source input/output unit  307  also passes sound waveform data received from volume control unit  306  to the sound source control I/F of OS  310 .  
         [0069]     Voice line input/output unit  308  converts the format of voice waveform data received from voice data processing unit  305  for voice communication, and sends the converted data to voice call line  106 . Voice line input/output unit  308  also converts the format of voice communication data received from voice communication line  106  such that the data can be reproduced on OS  310 , and passes the converted data to voice data processing unit  305 .  
         [0070]     Sound source using application  309  represents any application which uses a sound source, other than voice call application  301 , that runs on PC terminal  102 .  
         [0071]     OS system sound output control unit  311  generates system sound such as alarm sound, confirmation sound and the like associated with OS  310 , and sends the system sound to a sound source which has been set to reproduce the system sound.  
         [0072]     Each sound control I/F  312 ,  313  is an I/F for an application on OS  310  for controlling each sound source.  
         [0073]     Fixed storage device control unit  314  reads and writes data from/into fixed storage device  209  of PC terminal  102  in response to instructions of an application or OS  310 .  
         [0074]     Voice line I/F control unit  315  transmits/receives data to/from voice line I/F unit  203  of PC terminal  102  in response to instructions of an application or OS  310 .  
         [0075]     Each sound source volume control unit  316 ,  317  increases or decreases the volume of input/output sound waveform data for each sound source in accordance with a value indicated by OS  310 .  
         [0076]     Each sound source control unit  318 ,  319  receives/delivers data to/from a sound source connected to PC terminal  102  through sound source I/F unit  202 .  
         [0077]     Communication control unit  320  transmits/receives voice communication control signals to/from voice call line  106 , and controls sound sources through sound source control I/F&#39;s  312 ,  313 .  
         [0078]      FIG. 4  is a block diagram illustrating the configuration of handset sound source  207  connected to PC terminal  102 . Handset sound source  207  comprises handset unit  407  and base unit  408 , where handset unit  407  comprises handset sound input unit  404  and handset sound output unit  405 , while base unit  408  comprises PC I/F unit  401 , sound input/output switching unit  402 , base sound output unit  403 , and hook switch detection unit  406 .  
         [0079]     PC I/F unit  401  is connected to sound source I/F unit  202  of PC terminal  102  for transmitting/receiving data to/from PC terminal  102 .  
         [0080]     Sound input/output switching unit  402  switches depending on whether voice data transmitted/received to/from PC I/F unit  401  is connected to handset unit  407  or to base unit  408 .  
         [0081]     Base sound output unit  403  delivers voice data that is transmitted from PC terminal  102  and that is received through PC I/F unit  401  and voice input/output switching unit  402  to a speaker (not shown) of base unit  408  when sound input/output switching unit  402  is connected to base unit  408 .  
         [0082]     Handset sound input unit  404  transmits a sound input from the microphone of handset unit  407  to PC terminal  102  through sound input/output switching unit  402  and PC I/F unit  401  when sound input/output switching unit  402  is connected to handset unit  407 .  
         [0083]     Handset sound output unit  405  delivers sound data that is transmitted from PC terminal  102  and that is received through PC I/F unit  401  and sound input/output switching unit  402  to a speaker (not shown) of handset unit  407  when sound input/output switching unit  402  is connected to handset unit  407 .  
         [0084]     Hook switch detection unit  406  detects, with the aid of a hook switch (not shown) mounted in base unit  408 , whether handset unit  407  is hooked off or seated on base unit  408 , and notifies OS  310  of PC terminal  102  of the state of the hook switch through PC I/F unit  401  when the state of the hook switch changes in state.  
         [0085]      FIG. 5  is a diagram showing contents in a storage area for setting data in a setting data storage area for voice call application  301  stored in fixed storage device  209  of PC terminal  102 .  
         [0086]     Handset hook state  501  stores the state of the hook switch in handset sound source  207  that is connected to PC terminal  102 .  
         [0087]     Handset destination state  502  stores the state when sound input/output switching unit  402  in handset sound source  207  has switched.  
         [0088]     Exchanger calling state  503  stores the state of PC terminal  102 , i.e., the state notified by voice exchanger  101  indicating whether a telephone call (conversation) is taking place or not.  
         [0089]     Voice data transmission/reception state  504  stores the state of voice line I/F unit  203  in PC terminal  102 , indicating whether it is transmitting/receiving voice data to/from voice call line  106 .  
         [0090]     In-service ringer tone volume setting  505  stores the amount by which ringer tone volume control unit  304  of voice call application  301  increases or decrease the volume when an incoming call arrives at PC terminal  102  while a conversation is occurring.  
         [0091]     In-service OS/other application volume setting  506  stores the amount by which voice call application  301  increases or decreases the volume for sound source volume control units  316 ,  317  of OS  310  when a conversation is occurring at PC terminal  102 .  
         [0092]     Call sound source setting  507  stores the ID of a sound source that has been instructed by voice call application  301  to transmit/receive voice data to/from voice call line  106 .  
         [0093]     Incoming call sound source setting  508  stores the ID of a sound source which that has been instructed by voice call application  301  to generate a ringer tone.  
         [0094]     Next, the operation of this embodiment will be described with reference to flow charts illustrated in  FIGS. 6 and 7 .  
         [0095]     A description will be first given of a scenario where it is determined, based on the state of the hook switch in handset sound source  207 , whether or not a conversation is occurring at PC terminal  102 , and the volume of the ringer tone is decreased to a set value when the ringer tone is generated during the conversation by the same sound source which is used in the conversation.  
         [0096]     Assume that handset sound source  207  alone is connected to sound source I/F unit  202 , the ID of handset sound source  207  is set in call sound source setting  507 , and the ID of handset sound source  207  is also set in ringer tone source setting  508 . In addition, assume that a volume reduction value (−5 dB) is set in in-service ringer tone volume setting  505 .  
         [0097]     Sound input/output switching unit  402  of handset sound source  207  is switched to handset unit  407  by communication control unit  302  through sound source input/output unit  307 , sound source control I/F  312 , sound source control unit  318 , and PC I/F unit  401  upon the start of a call.  
         [0098]     PC terminal  102  is in connection with voice call network  104  for making a call using handset sound source  207 , so that handset unit  407  is hooked off base unit  408 . This state of handset unit  407  is detected by hook switch detection unit  406  (step B 1  in  FIG. 7 ), and notified to PC I/F unit  401 , sound source I/F unit  202  and CPU  204  of PC terminal  102  and to sound source control unit  318 , sound source control I/F unit  312 , and communication control unit  320  of OS  310 . In response to the received notification of a change in the on-hook state of handset unit  407 , communication control unit  320  writes an off-hook state into handset hook state  501  through fixed storage device control unit  314  (step B 2  in  FIG. 7 ). Subsequently, it is confirmed that a ringer tone is generated (step B 3  in  FIG. 7 ), however, the flow terminates if no ringer tone is generated at this time.  
         [0099]     When voice exchanger  101  is notified of an incoming tall from voice communications network  104  to PC terminal  102 , voice exchanger  101  transmits a ringer tone generation command to PC terminal  102  through voice call line  106 . CPU  204  receives the ringer tone generation command through voice line I/F unit  203 , and processes the command in accordance with software running on OS  310 , i.e., voice call application  301  stored in memory  205 . Specifically, voice line I/F control unit  315  of OS  310  receives the ringer tone generation command, and passes the command to voice line input/output unit  308  of voice call application  301 . Voice line input/output unit  308  passes the ringer tone generation command to communication control unit  320  (step A 1  in  FIG. 6 ).  
         [0100]     Communication control unit  320  reads call sound source setting  507  through fixed storage device control unit  314 . Since the handset sound source is currently set in call sound source setting  507 , communication control unit  320  reads handset hook state  501  through fixed storage device control unit  314 . Communication control unit  310  determines that a call is in progress because handset hook state  501  is in an off-hook state (step A 2  in  FIG. 6 ).  
         [0101]     Subsequently, communication control unit  320  reads ringer tone source setting  508  through fixed storage device control unit  314 , and confirms, through sound source control I/F unit  312  and sound source control unit  318 , that a connection has been made between handset sound source  207  and the PC terminal and handset sound source  207  is set as a ringer tone source, i.e., handset sound source  207  is connected to PC terminal  102  (step A 3  in  FIG. 6 ).  
         [0102]     Subsequently, communication control unit  320  compares read call sound source setting  507  with ringer tone source setting  508  to determine that these settings indicate the same sound source (step A 4  in  FIG. 6 ).  
         [0103]     Next, communication control unit  320  reads in-service ringer tone volume setting  505  through fixed storage device control unit  314 , reads the volume reduction value (−5 dB), and transmits a ringer tone transmission command to ringer tone generation unit  303  together with the volume reduction value. Ringer tone generation unit  303  reads a ringer tone waveform file recorded in fixed storage device  209  through ringer tone file reading unit  302 , converts the file into format which permits the ringer tone to be reproduced on OS  310 , and sends the converted file to ringer tone volume control unit  304  together with the volume reduction value (step S 5  in  FIG. 6 ).  
         [0104]     Subsequently, ringer tone volume control unit  304  decreases the received ringer tone volume by the indicated volume reduction value, and transmits the resulting ringer tone waveform data to sound source input/output unit  307  through volume control u nit  306 . Sound source input/output unit  307  passes the ringer tone waveform data to sound source control I/F  312  to issue a ringer tone generation command. Upon receipt of the ringer tone waveform data through sound source control I/F  312 , sound source control unit  318  passes the ringer tone waveform data to handset sound source  207  through sound source I/F unit  202  and PC I/F unit  401 . Then, the ringer tone waveform data is passed to handset sound output unit  405  through sound input/output switching unit  402 , and the ringer tone is reproduced from the speaker of handset sound source  207  (step A 6 ).  
         [0105]     In this embodiment, it is determined at step A 2  that a call is in progress, but when the hook switch of the handset sound source is in an on-hook state, it is determined that no call is in progress, in which case the ringer tone generation command from communication control unit  320  is transmitted to volume control unit  304 , without including the volume reduction value, to generate the ringer tone at a normal volume at step A 6 .  
         [0106]     Also, in this embodiment, it is determined at step A 3  that the ringer tone source exists, but when no ringer tone source exists, processing at step A 4  is skipped, and at step A 5  onward, the call sound source is instructed to generate the ringer tone at a decreased volume in a similar manner to this embodiment.  
         [0107]     Further, in this embodiment, it is determined at step A 4  that the ringer tone source is the same as the call sound source, but when the ringer tone source is different from the call sound source, the ringer tone generation command from communication control unit  320  is transmitted to volume control unit  304 , without including the volume reduction value, to instruct the ringer tone source to generate the ringer tone at a normal volume at step A 6 .  
         [0108]     Further, in this embodiment, the calling state does not change while the ringer tone is beeping, but if the hook switch state is changed while the ringer tone is beeping, the flow proceeds from processing at step B 3  to processing at step B 4 , followed by execution of processing at step A 2 . In this way, upon transition to a calling state while the ringer tone is beeping, the ringer tone volume is decreased. After the calling state ends, the ringer tone volume is increased.  
         [0109]     In this embodiment configured as described above, even if the state of the sound source for generating the ringer tone in PC terminal  102  changes, a louder ringer tone will not be generated from a sound source which is being used in a conversation, so that the conversation is not hindered by the ringer tone.  
       Second Embodiment  
       [0110]     Next, a second embodiment of the present invention will be described.  
         [0111]     In the first embodiment, the value in in-service ringer tone volume setting  505  is a value in which the sound volume changes. Alternatively, the volume may be set to OFF, so that the ringer tone is not generated.  
         [0112]     In this scenario, the aforementioned flow is modified at step A 6 .  
         [0113]     Since the indicated volume is OFF, ringer tone volume control unit  304  transmits mute ringer tone waveform data to sound source input/output unit  307  through volume control unit  306 . Sound source input/output unit  307  passes the ringer tone waveform data to sound source control I/F  312  to issue a ringer tone generation command. Upon receipt of the ringer tone waveform data through sound source control I/F  312 , sound source control unit  318  passes the ringer tone waveform data to handset sound source  207  through sound source I/F unit  202  and PC I/F unit  401 . This data is further passed to handset sound output unit  405  through sound input/output switching unit  402  to reproduce the ringer tone from the speaker of the handset, but since the ringer tone is muted, no ringer tone beeps (step A 6 ).  
         [0114]     According to the second embodiment, the present invention can also be implemented if the user desires that not even a small ringer tone be emitted from the sound source during a conversation.  
       Third Embodiment  
       [0115]     Next, a third embodiment of the present invention will be described with reference to  FIG. 8 .  
         [0116]     In the first embodiment described above, the on/off state of the hook switch of handset sound source  207  is relied on to determine whether or not a call is in progress. Alternatively, this determination may be made at the destination of handset sound source  207 .  
         [0117]     In this scenario, processing at steps B 1 , B 2 , B 3 , B 4  is modified to the following operations as illustrated in a flow chart of  FIG. 8 .  
         [0118]     Sound input/output switching unit  402  of handset sound source  207  is switched to handset unit  407  by communication control unit  320  through sound source input/output unit  307 , sound source control I/F  312 , sound source control unit  318 , and PC I/F unit  401  upon the start of a call (step C 1  in  FIG. 8 ), and this state is written into handset destination state  502  by communication control unit  320  through fixed storage device control unit  315  (step C 2  in  FIG. 8 ). Subsequently, it is confirmed whether or not the on/off state of the hook switch has changed while the ringer tone is beeping (step C 3  in  FIG. 8 ). When the on/off state of the hook switch is changed while the ringer tone is beeping, the flow proceeds to processing at step C 4 , followed by the execution of processing at step A 2 . In this way, when a PC terminal goes into a state in which a telephone conversation is in progress while the ringer tone is beeping, the ringer tone volume is decreased. When this state ends, the ringer tone volume is increased.  
         [0119]     In addition, processing at step A 2  is modified in the following manner.  
         [0120]     Communication control unit  320  reads call sound source setting  507  through fixed storage device control unit  314 . Since call sound source setting  507  is currently set to the handset sound source, communication control unit  320  reads handset destination state  502  through fixed storage device control unit  314 . Communication control unit  320  determines that a call is in progress because the handset destination is set to the handset unit (step A 2 ).  
         [0121]     According to the third embodiment, the present invention can also be implemented even when a used handset sound source does not have a hook switch.  
       Fourth Embodiment  
       [0122]     Next, a fourth embodiment of the present invention will be described with reference to  FIG. 9 .  
         [0123]     In this embodiment, an exchanger calling state  503  is relied on to determine whether or not a call is in progress, where processing at steps B 1 , B 2 , B 3 , B 4  is modified to the following operations as illustrated in a flow chart of  FIG. 9 .  
         [0124]     When PC terminal  102  receives a call start/end command from voice exchanger  101  through voice line interface unit  203  (step D 1  in  FIG. 9 ), communication control unit  320  receives the contents of the command through voice line input/output unit  308  and voice line I/F control unit  305 , instructs voice data processing unit  305  to start/end a voice call, and simultaneously writes the calling state into exchanger calling state  503  through fixed storage device control unit  314  (step D 2  in  FIG. 9 ). Subsequently, communication control unit  320  confirms whether or not the exchanger calling state is changed while a ringer tone is beeping (step D 3  in  FIG. 9 ). When the exchanger calling state is changed while the ringer tone is beeping, the flow proceeds from processing at step D 3  to processing at step D 4 , followed by execution of the processing at step A 2 . In this way, when PC terminal  102  enters a state in which a call is in progress, while the ringer tone is beeping, the ringer tone volume is decreased. When the telephone conversation ends, the ringer tone volume is increased.  
         [0125]     In addition, processing at step A 2  is modified in the following manner.  
         [0126]     Communication control unit  320  reads exchanger calling state  503  through fixed storage device control unit  314 . Communication control unit  320  determines that a call is in progress because a calling state is indicated by read exchanger calling state  503  (step A 2 ).  
         [0127]     According to the fourth embodiment, the present invention can also be implemented even when a used handset sound source does not have a hook switch or a sound input/output switching function.  
       Fifth Embodiment  
       [0128]     Next, a fifth embodiment of the present invention will be described with reference to  FIG. 10 .  
         [0129]     In this embodiment, the voice data transmission/reception state is relied on to determine whether or not a call is in progress, in which the processing at steps B 1 , B 2 , B 3 , B 4  is modified to the following operations as illustrated in a flow chart of  FIG. 10 .  
         [0130]     Communication control unit  320  of PC terminal  102  always monitors a voice data transmission/reception state through voice line input/output unit  308  of voice data processing unit  305  (step E 1  in  FIG. 10 ), and writes the monitoring result into voice data transmission/reception state  504  through fixed storage device control unit  314  in accordance with the voice data transmission or reception state (step E 2  in  FIG. 10 ). Upon detection of the voice data transmission or reception state at step E 1 , communication control unit  320  writes an ongoing transmission/reception state into voice data transmission/reception state  504  through fixed storage device control unit  314  at step E 2 . On the other hand, when no voice data has been transmitted or received for a previously set certain time period at step E 1 , communication control unit  320  writes a transmission/reception interrupted state into voice data transmission/reception state  504  through fixed storage device control unit  314  at step E 2 .  
         [0131]     The ongoing transmission/reception state occur as well when mute voice data is being transmitted/received. Subsequently, communication control unit  320  confirms whether or not the voice data transmission/reception state has been changed while a ringer tone is beeping (step E 3  in  FIG. 10 ). When the voice data transmission/reception state has been changed while the ringer tone is beeping, the flow proceeds to processing at step E 4 , followed by execution of processing at step A 2 . In this way, as PC terminal  102  enters a state in which a call is in progress, the ringer tone volume is decreased. When the call in progress ends, the ringer tone volume is increased.  
         [0132]     In addition, processing at step A 2  is modified in the following manner.  
         [0133]     Communication control unit  320  reads voice data transmission/reception state  504  through fixed storage device control unit  314 . Communication control unit  320  determines that a call is in progress because an ongoing transmission/reception state is indicated by voice data transmission/reception state  504  (step A 2 ).  
         [0134]     According to the fifth embodiment, the present invention can also be implemented when no call start/end signal is supplied from the exchanger, and when a used handset sound source does not have a hook switch or a sound input/output switching function.  
       Sixth Embodiment  
       [0135]     Next, a sixth embodiment of the present invention will be described with reference to  FIG. 11 .  
         [0136]     In this embodiment, when the state of the call in progress is changed, the volume of OS-related sound is completely decreased, and the volume of sound associated with the voice call application and ringer tone is increased by the same amount that the OS-related sound is decreased, where processing at steps B 1 , B 2 , B 3 , B 4  is modified to the following operations as illustrated in a flow chart of  FIG. 11 .  
         [0137]     Processing at steps F 1 , F 2  is the same as that at steps B 1 , B 2 .  
         [0138]     Communication control unit  320  of PC terminal  102  writes an off-hook state into handset hook state  501  through fixed storage device control unit  314 , and simultaneously reads in-service OS/other application volume setting  506  (step F 3 ). When handset hook state  501  indicates an off-hook state, communication control unit  320  transmits this value to sound source volume control unit  316  through sound source control I/F  312  associated with a sound source which is set in call sound source setting  507 , and completely decreases the volume of sound associated with PC terminal  102 ,(step F 4 ). Then, communication control unit  320  reverses the sign (plus or minus) of the value in in-service OS/other application volume setting  506 , transmits the resulting value to volume control unit  306 , and completely increases the volume of the voice call application (step F 5 ).  
         [0139]     Processing at steps F 6 , F 7  is the same as that at step B 3 , B 4 , respectively.  
         [0140]     In the sixth embodiment configured as described above, PC terminal  102  can be additionally provided with a function of decreasing the volume of system sound associated with the OS, or the volume of sound generated by another sound source using application  309 , if generated from a sound source during a conversation without affecting at all the volume of voices during the conversation, and the volume of the in-service ringer tone in the foregoing embodiments. Accordingly, the conversation is not affected by sound associated with the OS and other applications, which can leak from a sound source used in the conversation, while a call is in progress.  
       Seventh Embodiment  
       [0141]     Next, a seventh embodiment of the present invention will be described with reference to  FIG. 12 .  
         [0142]     In this embodiment, processing at steps F 1  and F 2  in the sixth embodiment is replaced with processing similar to that at steps C 1  and C 2  in the third embodiment.  FIG. 12  is a flow chart illustrating such a processing operation. Processing performed at steps G 1 , G 2  in  FIG. 12  is similar to that at steps C 1 , C 2  in the third embodiment, and processing performed at steps G 3 -G 7  is similar to that at steps F 3 -F 7  in the sixth embodiment.  
         [0143]     According to the seventh embodiment, the present invention can also be implemented even when a used handset sound source does not have a hook switch.  
       Eighth Embodiment  
       [0144]     Next, an eighth embodiment of the present invention will be described with reference to  FIG. 13 .  
         [0145]     In this embodiment, processing at steps F 1  and F 2  in the sixth embodiment is replaced with processing similar to that at steps D 1  and D 2  in the fourth embodiment.  FIG. 13  is a flow chart illustrating such processing operations. Processing performed at steps H 1 , H 2  in  FIG. 13  is similar to that at steps D 1 , D 2  in the fourth embodiment, and processing performed at steps H 3 -H 7  is similar to that at steps F 3 -F 7  in the sixth embodiment.  
         [0146]     In the eighth embodiment, the present invention can also be implemented when a used handset sound source does not have a hook switch or a sound input/output switching function.  
       Ninth Embodiment  
       [0147]     Next, a ninth embodiment of the present invention will be described with reference to  FIG. 14 .  
         [0148]     In this embodiment, processing at steps F 1  and F 2  in the sixth embodiment is replaced with processing similar to that at steps E 1  and E 2  in the fifth embodiment.  FIG. 14  is a flow chart illustrating such processing operations. Processing performed at steps I 1 , I 2  in  FIG. 14  is similar to that at steps E 1 , E 2  in the fourth embodiment, and processing performed at steps H 3 -H 7  is similar to that at steps F 3 -F 7  in the sixth embodiment.  
         [0149]     According to the ninth embodiment, the present invention can also be implemented even when no call start/end signal is supplied from the exchanger, and even when a used handset sound source does not have a hook switch or a sound input/output switching function.