Abstract:
When an incoming call to a wireless communication apparatus is detected, a wireless control apparatus uses a wireless link, which has been established by previous communication, to perform succeeding communication. Examples of communication include communication of audio or data already completed, or, when there are a plurality of wireless communication apparatus, communication of control information by a wireless link established when notification of an incoming call is given to the wireless communication apparatus.

Description:
This application is a division of application Ser. No. 08/622,583, filed on Mar. 28, 1996. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to a wireless control apparatus wirelessly connected to a wireless communication apparatus, as well as to a system comprising the wireless communication apparatus and the wireless control apparatus. 
   2. Description of the Related Art 
   A wireless communication system known in the art comprises a wireless control apparatus (master) and a wireless communication apparatus (slave) wirelessly connected to the wireless control apparatus. 
   When a transmission request is issued from the slave side or an incoming call is terminated at the slave side in a wireless communication system of this kind, the master searches for and decides upon the communication channel used in this communication between the master and slave and so notifies the slave using a control channel, whereupon the slave is shifted to the communication channel of which it has been notified, thereby establishing a wireless link. 
   When communication ends, control for the purpose of cutting off the wireless link is carried out over a prescribed period of time, whereupon the wireless link is cut. 
   However, when an incoming call to the slave is detected after communication ends, the wireless link is cut temporarily. This is despite the fact that the wireless link has hot been cut through the link cutting control operation because this operation is still in progress. This means that a new control channel is temporarily occupied to search for and decide upon an idle communication channel and establish a wireless link anew, whereupon communication commences. This procedure takes time. Moreover, if the wireless link cannot be established the second time, it may not be possible to perform communication in response to the incoming call. 
   Further, in order to make all slaves ring at the time of an incoming call from a communication line in a situation where a plurality of slaves exist, wireless links are established to all of the slaves. If an outgoing call is then abandoned by disconnection on the calling side, the wireless links to the slaves are cut. Or, if a slave responds to the incoming call, the wireless links to slaves other than the responding slave are disconnected. 
   Accordingly, if a party not sought by the calling side answers the incoming call, it is required that the call be transferred. When the transfer is made, the slave that is the destination of the transfer must re-establish the wireless link and the calling party is made to wait until this is achieved. 
   In particular, when there is an incoming call from another outside line or an outgoing call to a communication apparatus of another extension in the case of communication apparatus or private branch exchange accommodating a plurality of communication lines (outside lines) and also having a number of extensions, there are instances where a procedure for establishing a wireless link with the other communication apparatus is made to wait while a procedure for establishing a wireless link is being executed for the incoming call or outgoing call. It may take several seconds or more before the communication apparatus that is the destination of the transfer answers or before there is a hold response made by the other communication apparatus. The result is poor operability. 
   SUMMARY OF THE INVENTION 
   Accordingly, an object of the present invention is to eliminate the troublesome task of re-establishing a wireless link and use an already established wireless link as is in a case where an incoming call arrives at a wireless communication terminal after the end of communication, thereby making it possible to start communication rapidly without occupying a control channel for a fixed period of time for the purpose of establishing the wireless link. 
   Another object of the present invention is to maintain a wireless link for a period of time longer than that required to disconnect the wireless link after communication ends. 
   A further object of the present invention is to provide a wireless communication system in which, in an instance where a calling party receives a response from a party different from the intended party after the incoming call from a public telephone line is terminated and answered, as is often the case where a hold-and-transfer operation is used most frequently, the operation for effecting transfer to another communication terminal or for holding and answering at another communication terminal is facilitated. 
   Still another object of the present invention is to make it possible to adjust the time needed to disconnect a wireless link after communication ends. 
   Still another object of the present invention is to make it possible to adjust the time needed to disconnect the wireless link of a communication terminal other than a communication terminal that has responded to an incoming call, the purpose being to achieve a speedy transfer to the other communication terminal after an incoming call from a telephone line to a plurality of wireless communication terminals is terminated and answered or to achieve a prompt holding response at the other communication terminal. 
   Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram illustrating the construction of a wireless telephone system according to a first embodiment of the present invention; 
       FIG. 2  is a sequence chart showing an example of operation of the wireless telephone system according to the first embodiment; 
       FIG. 3  is a flowchart showing an example of the operation of a main unit according to the first embodiment; 
       FIG. 4  is a flowchart showing an example of the operation of a slave according to the first embodiment; 
       FIG. 5  is a block diagram illustrating the construction of a wireless telephone system according to a second embodiment of the present invention; 
       FIG. 6  is a sequence chart showing an example of operation of the wireless telephone system according to the second embodiment; 
       FIG. 7  is a block diagram illustrating the construction of a wireless telephone system according to a third embodiment of the present invention; 
       FIG. 8  is a sequence chart showing an example of operation of the wireless telephone system according to the third embodiment; 
       FIG. 9  is a flowchart showing an example of the operation of a communication control apparatus according to the third embodiment; 
       FIG. 10  is a flowchart showing an example of the operation of a master according to the third embodiment; 
       FIG. 11  is a block diagram showing a cordless key telephone system according to a fourth embodiment of the present invention; 
       FIG. 12  is a block diagram showing the construction of a dedicated extension cordless key telephone according to the fourth embodiment of the present invention; 
       FIG. 13  is a flowchart showing an operation in which a main unit stores the status that prevails when a wireless link is connected in the fourth embodiment; 
       FIG. 14  is a flowchart showing an operation performed when a wireless link is disconnected in the fourth embodiment; 
       FIG. 15  is a sequence chart showing operation up to response and holding of an incoming call to an outside line in the fourth embodiment; 
       FIG. 16  is a sequence chart showing operation when a hold response is made from a state in which a wireless link is disconnected in the fourth embodiment; 
       FIG. 17  is a sequence chart showing operation when made from a state in which a wireless link is disconnected in the fourth embodiment; 
       FIG. 18  is a flowchart showing operation of a dedicated extension cordless telephone at the time of a made in the fourth embodiment; 
       FIG. 19  is a flowchart showing an operation in which a wireless link with a cordless telephone is not cut during acquisition of a telephone line when a terminate-and-answer operation has been detected in a fifth embodiment of the present invention; 
       FIG. 20  is a block diagram illustrating the construction of a system according to a sixth embodiment of the present invention; 
       FIG. 21  is a flowchart showing operation of a main unit according to the sixth embodiment; 
       FIG. 22  is a block diagram showing the construction of a main unit according to a seventh embodiment of the invention; and 
       FIG. 23  is a block diagram showing the construction of a control panel according to the seventh embodiment of the invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Preferred embodiments of the present invention will now be described in detail with reference to the drawings. 
     FIG. 1  is a block diagram showing a wireless telephone system according to a first embodiment of the present invention. 
   This system comprises a cordless slave (referred to as a “slave” below)  1 , i.e., a wireless slave, and a key telephone master (referred to as a “main unit” below)  2 . 
   The slave  1  has a memory  110  for processing and stores a call end-processor  111 , an incoming-call processor  112  and a call processor  113 , an operational controller  120  for supervising control of the slave, a wireless unit  130  for supervising wireless connection and disconnection between the slave and the main unit  2 , a lamp display  140  which flashes a main-wire lamp for an incoming call to an outside line; an LCD display  150  for displaying the telephone number of an incoming call to an outside line, and a transmitter/receiver  160  for transmitting and receiving (talking and listening). 
   The main unit  2  has a memory  210  which stores a terminating/transmitting processor  211 , a call-end processor  212  and a call processor  213 , an operational controller  220  for supervising control of the main unit, a wireless unit  230  for supervising wireless connection and disconnection between the main unit  2  and a slave, a communication-line controller  240  for managing or controlling a main wire such as a public telephone line, and a wireless-link disconnect timer  250 . The timer  250  may be implemented by executing program processing within the operational controller  220 . 
     FIG. 2  is a sequence chart showing an example of operation of the wireless telephone system according to the first embodiment, and  FIG. 3  is a flowchart showing an example of the operation of the main unit  2  according to the first embodiment. 
   As shown at step  301  in  FIG. 3 , the operational controller  220  starts up the call processor  213  within the memory  210  to execute call processing. If, during this processing, notification that slave  1   a  is on the hook is received via the wireless unit  230  at step  303  without detection of an incoming call to the slave  1   a  at step  302 , the operational controller  220  starts up the call-end processor  212  in memory  210  at step  304  and transmits a standby-state transition request, which is for placing the master on standby while maintaining the established wireless link, to the slave  1  at step  305  via the wireless unit  230  under the command of the operational controller  220 . At this time the main unit  2  determines at step  306  whether or not there is an incoming call to the slave  1   a . If there is no incoming call, the wireless-link disconnect timer  250 , which is for disconnecting the wireless link upon elapse of a prescribed period of time, is started at step  307  in response to a command from the operational controller  220 . If there is an incoming call (“YES” at step  309 ) to the slave  1   a  before the timer runs out of time (“NO” at step  308 ), the operational controller  220  resets the wireless-link disconnect timer  250 , starts the terminating/transmitting processor  211  in the memory  210  and, in order to notify the slave  1   a  of the incoming call, sends an outside-line terminate request to the slave  1   a  at step  310  using the wireless link already established by the preceding call via the wireless unit  230 . Then, if notification of the fact that the slave  1   a  has been taken off the hook is received from the slave  1   a  at step  311  by the wireless link that was being used by the preceding call, the operational controller  220  starts the call processor  213  in the memory  210  and executes processing (step  312 ) for calling the slave  1   a  using the wireless link already established by the preceding call via the wireless unit  230 . 
   If an incoming call to the slave  1   a  is detected at step  306  when notification of the end of the call has been received from the slave  1   a , the operational controller  220  starts the terminating/transmitting processor  211  in the memory  210  and sends the outside-line terminate request to the slave  1   a  via the wireless unit  230  at step  310  using the wireless link already established by the preceding call. Thereafter, if notification of the fact that the slave  1   a  is off the hook is received from the slave  1   a  at step  311 , the operational controller  220  starts the call processor  213  in the memory  210  to execute call processing (step  312 ) with respect to the slave  1   a.    
   If the fact that the timer  250  has run out of time is detected by the operational controller  220  at step  308 , then, in order to disconnect the wireless link, the operational controller  220  sends a wireless-link disconnect request to the slave  1   a  via the wireless link  230  at step  313  and disconnects the wireless link at step  315  when confirmation of wireless-line disconnection from the slave  1   a  is received via the wireless unit  230  at step  314 . 
   If an incoming call is detected (as by a telephone beeper service) at step  302  during communication, the operational controller  220  sends the slave  1   a , via the wireless unit  230 , the outside-line terminate request to inform the slave  1   a  of the incoming call (step  316 ). If notification that slave  1   a  is off the hook is received from the slave  1   a  (step  317 ), then the operational controller  220  sends notification of this fact to the exchange via the public telephone line (step  318 ). The exchange places the call on hold and transmits a call signal with regard to the terminating call. As a result, the operational controller  220  executes call processing (step  319 ) with respect to the slave  1   a  using the established wireless link as is. When notification of the fact that the slave  1   a  is on the hook is received again (step  320 ), the operational controller  220  communicates this fact to the exchange (step  321 ) so that the call that was in the held state is started again. 
     FIG. 4  is a flowchart showing operation of the slave  1   a  according to this embodiment. 
   In  FIG. 4 , the operational controller  120  starts the call processor  113  in memory  110  and executes call processing at step  401  using the transmitter/receiver  160  and wireless unit  130 . If the handset of the transmitter/receiver  160  is on the hook (“YES” at step  402 ), the operational controller  120  so notifies the main unit  2  (step  403 ) via the wireless unit  130 . If beeper service is being received, the call processing in response to the incoming call is continued (step  404 ) using the established wireless link. If beeper service is not being received, however, the operational controller  120  of the slave  1   a  that has received a standby-state transition request (step  405 ) from the main unit  2  via the wireless unit  130  starts the call-end processor  111  in memory  110  at step  406  and causes the LDC display unit  150  to present a display indicative of the standby state at step  407 . The operational controller  120  then undergoes a transition to the standby state. 
   The wireless link that was being used in the preceding call is kept as is until the wireless-link disconnect request is received from the main unit  2 . 
   Upon receiving notification of outside line termination from the main unit  2  via the wireless unit  130  at step  408 , the operational controller  120  starts the incoming-call processor  112  in memory  110  at step  409  and causes the LDC display unit  150  and lamp display unit  140  to display the fact that the incoming line has arrived at the outside line (step  410 ). 
   When the operator observes the LDC display unit  150  and lamp display unit  140  and takes the phone off the hook at step  411 , the operational controller  120  transmits notification of this fact to the main unit  2  (step  412 ) using the wireless link that was being used in the preceding call and then starts the call processor  113  in memory  110  to execute call processing with regard to the above-mentioned outside line (step  413 ). 
   If notification of the incoming call to the outside line is not received from the main unit  2  at step  408  the wireless-link disconnect request is received from the wireless unit  130  at step  414 , the operational controller  120  transmits a wireless-link disconnect confirmation signal to the main unit  2  via the wireless unit  130  at step  415  to disconnect the wireless link at step  416 . 
     FIG. 5  is a block diagram based upon a wireless system according to a second embodiment of the invention. 
   The system of  FIG. 5  differs from that of  FIG. 1  in that a cordless master (referred to as a “master” below)  3  serving as a wireless master is connected to the main unit  2  by a wire line  2 , with the master  3  being provided internally with a transfer section  310  for transfer of wireless communication between the main unit  2  and the slave  1 . Other components are similar to those of the first embodiment ( FIG. 1 ) and need not be described again. 
     FIG. 6  is a sequence chart showing an example of operation of the wireless telephone system according to this embodiment. 
   The master  3  relays wireless communication between the main unit  2  and slave  1  by using the transfer section  310 , thereby effecting a transfer operation. The operation of the main unit  2  and each of slaves  1   a ˜ 1 N is the same as in the first embodiment and need not be described again. 
   If the cord length between the main unit  2  and master  3  is extended by adopting an arrangement of the kind shown in  FIG. 5 , the slaves  1  can be deployed over a wider area. 
     FIG. 7  is a block diagram illustrating a third embodiment of the present invention. 
   In this embodiment, as shown in  FIG. 7 , the wireless unit in the main unit  2  is eliminated, and the master  3  is provided with a memory  310  storing a terminating/transmitting processor  311 , an operational controller  320  for supervising control of the master  3 , a wireless unit  300  for performing wireless connection and disconnection between the master  3  and a slaves  1 , and a timer  340 . Other components are similar to those of the second embodiment shown in  FIG. 5 . 
   Thus, the third embodiment is characterized by the fact that the sections for processing relating to connection of the wireless link are provided in the master  3  to execute this processing. 
     FIG. 8  is a sequence chart showing an example of operation of the wireless system according to the embodiment of the invention. 
     FIG. 9  is a flowchart showing an example of the operation of the communication control apparatus  2  according to this embodiment. 
   As shown at step  901  in  FIG. 9 , the operational controller  220  executes call processing with respect to the slaves  1 . If, during this processing, notification that slave  1   a  is on the hook is received via the master  3  at step  903  without detection of an incoming call to the slave  1   a  at step  902 , the operational controller  220  starts up the call-end processor  212  in memory  210  at step  904  and transmits a standby-state transition request to the master  3  at step  905 . 
   If there is an incoming call to the slave  1   a  at step  906 , the operational controller  220  starts the terminating/transmitting processor  211  in the memory  210  and transmits an outside-line terminate request to the master  3  at step  907 . Then, if notification of the fact that the slave  1   a  has been taken off the hook is received from the master  3  at step  908 , the operational controller  220  starts the call processor  213  in the memory  210  and executes processing (step  909 ) for calling the slave  1   a.    
   If an incoming call to the slave  1   a  is detected at step  902 , the operational controller  220  sends the outside-line terminate request to the master  3  at step  910 . If notification of the fact that the slave  1   a  is on the hook is received from the slave  1   a  at step  911 , the operational controller  220  notifies the exchange of this fact via the public telephone line at step  912  and executes call processing with respect to the incoming call at step  913 . 
   When notification of the fact that the slave is on the hook is received again (step  914 ), the operational controller  220  communicates this fact to the exchange (step  915 ) and executes call processing for calling the slave  1   a.    
     FIG. 10  is a flowchart showing an example of operation of the master  3  according to this embodiment. 
   Processing (step  1001 ) for relaying communication between the slave  1   a  and communication control apparatus  2  is performed by the wireless unit  330  in response to a command from the operational controller  320 . If notification of the fact that the slave  1   a  is on the hook is received from the slave  1   a  (“YES” at step  1003 ) without the outside-line terminate request being sent from the communication control apparatus (“NO” at step  1002 ), notification of the fact that the slave  1   a  is on the hook is transferred to the communication control apparatus  2  (step  1004 ). If the standby-state transition request is subsequently received from the communication control apparatus at step  1005 , the operational controller  320  starts the wireless-link disconnect timer  340  at step  1006  and transmits the standby-state transition request to the slave  1   a  via the wireless unit  330  at step  1007 . If the outside-line terminate request is received from the communication control apparatus  2  at step  1009  before the timer  340  runs out of time (“NO” at step  1008 ), the operational controller  320  starts the terminating/transmitting processor  311  in memory  310  at step  1010  and transmits the outside-line terminate request to the slave  1   a  at step  1011  using the wireless link that was being used in the preceding call. 
   If notification that the slave  1   a  is off the hook is subsequently received from the slave via the wireless unit  330  (“YES” at step  1012 ), the operational controller  320  transfers notification of this event to the communication control apparatus  2  (step  1013 ) and executes processing (step  1001 ) for the relay operation between the slave  1   a  and the communication control apparatus  2 . 
   If the timer runs out of time (“YES” at step  1008 ) before the outside-line terminate request is received, the operational controller  320  transmits the wireless-link disconnect request to the slave  1   a  (step  1014 ) via the wireless unit  330  by the wireless link that was being used in the preceding call. If confirmation of disconnection of the wireless link is received from the slave  1   a  via the wireless unit  330  by the wireless link that was being used in the preceding call (step  1015 ), the operational controller  320  disconnects the wireless link at step  1016 . 
   If the outside-line terminate request is sent from the communication control apparatus during relay processing (“YES” at step  1002 ), the request is transmitted to the slave  1   a  (step  1017 ). If notification that the slave  1   a  is on the hook is received from the slave (“YES” at step  1018 ), notification of this fact is transmitted to the communication control apparatus at step  1019 . When transfer of this notification is finished, processing (step  1020 ) for relaying the communication between the communication apparatus and the slave  1   a  is performed using the established wireless link. 
   When notification that the slave  1   a  is on the hook is received (“YES” at step  1021 ), notification of this fact is transmitted to the communication control apparatus at step  1022  and relay processing is executed again. 
   The operation of the slave  1   a  is similar to that of the first embodiment and need not be described again. 
   By adopting this embodiment, the processing relating to the wireless link is executed almost entirely within the master  3 . As a result, the communication control apparatus  2  can transmit commands without taking the status of the wireless link into account, and it will suffice to provide the same program irrespective of processing of a wired telephone. A particular advantage of this invention is that it is possible to create the program of the communication control apparatus  2  without being aware of the fact that the telephone is a wireless telephone. 
   The first, second and third embodiments are described in conjunction with an incoming call to an outside line. However, if the system is one in which a call can be placed to an extension, the same effects can be obtained by performing a similar operation when the incoming call is to the extension. 
   Further, the method of wireless control in  FIGS. 1 ,  5  and  7  may be in accordance with the system ID method or an individual ID method. Though a call is described as being an outside line call in the first, second and third embodiments, calls may be extension calls, door intercom calls or private branch calls. 
   Further, though the first, second and third embodiments are described with regard to wireless telephone calls, the same effects can be obtained by applying the present invention to a wireless communication system in which data communication or the like is performed wirelessly. 
   Further, if an arrangement is adopted in which the times to which the timers  250 ,  340  of the first, second and third embodiments are set can be adjusted by an external operation, a system conforming to various applications can be provided. 
   Thus, in accordance with the embodiments of the invention as described above, if an incoming call arrives at a wireless communication apparatus while the wireless communication apparatus is performing communication or within a prescribed period of time from the end of communication, the wireless link that was established by such communication can be utilized as is, i.e., without being disconnected. As a result, notification of the incoming call and telephone communication can be carried out smoothly without the task of establishing a wireless link anew for the next communication operation and without taking too much time. 
     FIG. 11  is a block diagram showing the construction of a cordless key telephone system according to a fourth embodiment of the present invention. 
   A key telephone apparatus has a main unit  1102  which includes a switching section for switching voice calls and the like, outside-line controllers  1104   a ,  1104   b , which accommodate a public switched telephone network (PSTN)  1101 , for detecting an incoming call from a telephone line and sending a dialed number to a telephone line, extension wireless controllers  1105   a ,  1105   b  for controlling dedicated extension cordless telephones  1110   a ,  1110   b , respectively, a sound source  1106  for generating a DTMF signal sent to a telephone line, a holding tone and various other tones, a main controller  1107  for controlling the cordless key telephone apparatus in various ways, a ROM  1108  storing a control program for controlling a timer used in this embodiment as well as the overall main unit  1102 , and a RAM  1109  for storing various data. 
   The dedicated cordless telephones  1110   a ,  1110   b  are connected to the main unit  1102  by wireless links that have been established by a control channel. 
     FIG. 12  is a block diagram showing the internal construction of the dedicated extension cordless key telephones  1110   a ,  1110   b.    
   As shown in  FIG. 12 , the dedicated extension cordless key telephone  1110  includes an antenna  1202  for sending and receiving radio waves, a wireless controller  1203  for sending and receiving radio waves to and from the main unit and detecting whether a wireless link with the main unit has been established, an audio processor  1204  for linking a voice between the main unit and a handset and for sending and receiving control data to and from the main unit, a main controller  1205  for controlling this mobile device in various ways, a ROM  1206  in which a control program and the like are stored, a RAM  1207  for storing various data, an earphone  1208 , a microphone  1209 , a control panel  1210  having outside-line buttons, push buttons for dialing and a hold button, etc., a display unit  1211  comprising a liquid-crystal display device or LEDs (light-emitting diodes), and a speaker  1212  for sending an incoming-call tone. 
   When the dedicated extension cordless key telephone  1110   a  is taken off the hook in order to make a transmission to the PSTN  1101 , a procedure for establishing a wireless link between the dedicated extension cordless key telephone  1110   a  and the extension wireless controller  1105  is executed. After the wireless link is established, off-hook information is transmitted from the dedicated extension cordless key telephone  1110   a  to the extension wireless controller  1105   a.    
   Upon receiving the off-hook information from the dedicated extension cordless key telephone  1110   a , the extension wireless controller  1105   a  communicates this information to the main controller  1107 . 
   Upon receiving the off-hook information, from the dedicated extension cordless key telephone  1110   a , sent by the extension wireless controller  1105   a , the main controller  1107  causes the outside-line controller  1104   a  to acquire a telephone line. 
   Thereafter, when a dial button on the dedicated extension cordless key telephone  1110   a  is pushed, a dialing signal is sent to the extension wireless controller  1105   a  by the established wireless link, the extension wireless controller  1105   a  communicates the dialing signal to the main controller  1107 , and the latter sends the signal from the outside-line controller  1104   a  to the telephone line. 
   When the subscriber&#39;s number of the communicating party (not shown) has been dialed in full, the number is terminated at the communicating party and the party answers, it becomes possible for the communicating party to communicate with the dedicated extension cordless key telephone  1110   a  via the PSTN  1101  and the outside-line controller  1104   a , switching section  1103  and extension wireless controller  1105  in the main unit  1102 . 
   When there is an incoming call from a telephone line, the outside-line controller  1104   a  detects the incoming call and communicates the incoming-call information to the main controller  1107 . 
   Upon being notified of the incoming-call information, the main controller  1107  establishes a wireless link between the extension wireless controllers  1105   a  and  1105   b  and the dedicated extension cordless key telephones  1110   a ,  1110   b  in order to produce an incoming-call tone. 
   The extension wireless controllers  1105   a  and  1105   b  execute a procedure for establishing a wireless link with the dedicated extension cordless key telephones  1110   a  and  1110   b . When this procedure is completed, the extension wireless controllers  1105   a  and  1105   b  communicate establishment-completed information to the main controller  1107 . 
   Upon receiving the establishment-completed information, the main controller  1107  causes the extension wireless controllers  1105   a ,  1105   b  to send incoming-call information to the dedicated extension cordless key telephones  1110   a ,  1110   b.    
   Furthermore, the main controller  1107  transmits; the incoming-call tone from the sound source  1106  to the dedicated extension cordless key telephones  1110   a ,  1110   b  via the switching section  1103  and extension wireless controllers  1105   a ,  1105   b  so that the incoming-call tone is produced by the speaker  1212  of each of the dedicated extension cordless key telephones  1110   a  and  1110   b.    
   When the dedicated extension cordless key telephone  1110   b  is taken off the hook in response to the incoming call, an operation similar to that performed at the time of transmission is carried out. Specifically, the off-hook information is transmitted, this information is communicated from the extension wireless controller  1105   b  to the main controller  1107 , the main controller  1107  causes the outside-line controller  1104   a  to acquire a telephone line, a response is made to the incoming call and communication with the originating party (not shown) can be achieved in the same manner as at the time of transmission. 
   Next, an operation for storing the status of the main unit  1102  when a wireless link is established will be described in conjunction with the flowchart of  FIG. 13 . 
   In a state in which a wireless link has not been established between the extension wireless controller  1105   a  and the dedicated extension cordless key telephone  1110   a , the main controller  1107  waits for notification of the off-hook information, from the dedicated extension cordless key telephone  1110   a , sent by the extension wireless controller  1105   a  (step S 1301 ). If the information is not communicated to the main controller  1107 , the main controller  1107  waits for notification of incoming-call information, from the telephone line, sent by the outside-line controller  1104   a  (step S 1302 ). If the incoming-call information is not received, the program returns to step S 1301 . 
   If the off-hook information from the dedicated extension cordless key telephone  1110   a  has been communicated at step S 1301 , the fact that a connection has been made by the off-hook operation is stored in the RAM  1109  as the status at the time the wireless link is established (step S 1306 ). A transition is then made to the transmission state (step S 1307 ). 
   If the incoming-call information indicative of the incoming call to the outside line is communicated at step S 1302 , then the fact that an incoming-call connection has been made is stored in the RAM  1109  as the status at the time the wireless link is established (step S 1303 ) and the extension wireless controller  1105   a  is made to execute the procedure for establishing the wireless link (step S 1304 ). A transition is then made to step S 1305 , at which completion of wireless-link establishment is awaited. 
   Thus, status at establishment of the wireless link with a dedicated extension cordless key telephone is stored in the RAM  1109  by the main unit  1102 . 
   The operation of main unit  1102  when a wireless link is cut will now be described in conjunction with the flowchart of  FIG. 14 . 
   When the extension wireless controller  1105   a  and the dedicated extension cordless key telephone  1110   a  are wirelessly linked, the main controller  1107  monitors the hook status of the dedicated extension cordless key telephone  1110   a  (step S 1401 ). If the telephone is off the hook, the program returns to step S 1401 . If the telephone is on the hook, the main controller  1107  monitors the incoming-call status of the outside line (step S 1402 ). If an incoming call is still in progress, the program returns to step  1401 . If there is no incoming call, the main controller  1107  checks a disconnect timer (step  1403 ). If the timer is not operating, the main controller  1107  checks the status, stored in the RAM  1109 , that prevailed when the wireless link was established (step S 1404 ). In case of an off-hook connection, namely disconnection due to placing the telephone on the hook, the main controller  1107  starts a timer T 1  (e.g., 5 sec) (step S 1405 ). In case of an incoming-call connection, the main controller  1107  checks whether the incoming call was suspended (step S 1406 ). If the call was abandoned from the originating side in mid-course, the program proceeds to step S 1405 , where the disconnect timer T 1  is started. 
   If the call from the originating side is not abandoned at step S 1406  and the dedicated extension cordless key telephone  1110   b  responds to the incoming call, the main controller  1107  starts a disconnect timer T 2  (e.g., 20 sec), which has been set to a time longer than that of the disconnect timer T 1 , and the program returns to step S 1401 . 
   If the disconnect timer has already been started at step S 1403 , the timer performs a counting operation (step S 1408 ) and the program returns to step S 1401  if the timer has not run out of time. If the timer has run out of time, the timer is halted and a procedure for cutting the wireless link is started (step S 1409 ), after which the program makes a transition to step S 1410  to wait for completion of the wireless-link disconnection. 
   It should be noted that the timer simply performs a counting operation at step S 1408 . However, if the timer value is set and time is counted down when the disconnect timer T 1  or T 2  is started, it is possible to execute processing regardless of whether the timer that has started is T 1  or T 2 . 
   Thus, it is so arranged that when an operation for responding to an incoming call is detected, the wireless link with the extension cordless telephone is cut after a prescribed period of time which is longer than that when an outgoing call is abandoned in mid-course or when the telephone is placed on the hook. 
   Operation up to the response to an incoming call to an outside line and the placing of an outside line on hold during a call will now be described in accordance with the sequence chart of  FIG. 15 . 
   When there is an incoming call from a public telephone line, the main controller  1107  transmits wireless-link establishment request information to the extension wireless controller  1105   a  ( 1501 ,  1502 ). 
   Upon receiving the wireless-link establishment request information ( 1501 ,  1502 ), the extension wireless controller  1105  transmits a wireless-link establishment signal ( 1503 ) to the extension cordless telephone  1110   a  by a control channel. 
   At this time the call channel used between the extension wireless controller  1105   a  and the extension cordless telephone  1110   a  is communicated by the wireless-link establishment signal ( 1503 ) and the radio-wave receiving section is switched over to the call channel, thereby establishing a wireless link. 
   Meanwhile, since the control channel is already being used, the extension wireless controller  1105   b  waits for the control channel to become idle. 
   Upon receiving the wireless-link establishment signal ( 1503 ), the extension cordless telephone  1110   a  transmits a wireless-link establishment notification signal ( 1504 ) by the designated call channel. 
   Upon receiving the wireless-link establishment notification signal ( 1504 ), the extension wireless controller  1105   a  transmits a wireless-link establishment response signal ( 1505 ) to the extension cordless telephone  1110   a  and transmits wireless-link establishment confirmation information ( 1506 ) to the main controller  1107 , thereby notifying of the fact that the wireless link has been established. 
   The extension wireless controller  1105  detects the idle control channel, transmits a wireless-link establishment request signal ( 1507 ) to the extension cordless telephone  1110   b  by the control channel, notifies of the call channel to be used subsequently and switches the radio-wave receiving section over to the call channel, thereby establishing a wireless link. 
   Upon receiving the wireless-link establishment confirmation information ( 1506 ) from the extension wireless controller  1105   a , the main controller transmits outside-line incoming-call information ( 1508 ) to the extension wireless controller  1105   a . Upon receiving this information, the extension wireless controller  1105   a  transmits an outside-line incoming-call signal ( 1509 ), which includes an outside-line ringing tone and outside-line LED information, to the extension cordless telephone  1110   a.    
   Upon receiving the outside-line incoming-call signal ( 1509 ), the extension cordless telephone  1110   a  produces an outside-line incoming-call tone by the ringing tone designated by the outside-line incoming-call signal ( 1509 ) and causes outside-line LEDs to light in the pattern designated by the signal ( 1509 ). 
   After the wireless-link establishment request signal ( 1507 ) has been sent and received, the extension wireless controller  1105   b  and extension cordless telephone  1110   b  perform operations ( 1510 ˜ 1513 ) similar to those described above, cause the outside-line incoming-call tone to be produced by the extension cordless telephone  1110   b  and cause the outside-line LEDs to be lit. 
   Thereafter, when the extension cordless telephone  1110   a  is taken off the hook in order to answer the incoming call to the outside line, the extension cordless telephone  1110   a  transmits an off-hook signal ( 1514 ) to the extension wireless controller  1105   a , which in turn transmits off-hook information ( 1515 ) to the main controller  1107 . 
   Upon receiving the off-hook information ( 1515 ), the main controller  1107  causes: the outside-line controller  1104  to acquire the outside line terminating the call, connects the switching section  1103  and makes possible an outside-line call by the extension cordless telephone  1110   a.    
   Since the incoming call to the outside line has been responded to with regard to the extension cordless telephone  1110   b , it is necessary to halt the outside-line incoming-call tone and communicated new outside-line LED information. Accordingly, outside-line incoming-call abandonment information ( 1516 ) is transmitted to the extension wireless controller  1105  and the timer T 2 , which runs until the wireless link is cut off, is started. 
   Upon receiving the outside-line incoming-call abandonment information ( 1516 ), the extension wireless controller  1105   b  transmits an outside-line incoming-call abandonment signal ( 1517 ) to the extension cordless telephone  1110   b . Upon receiving the signal ( 1517 ), the extension cordless telephone  1110   b  halts the outside-line incoming-call tone and causes the outside-line LEDs to light in the pattern designated by the outside-line incoming-call abandonment signal ( 1517 ). 
   Thereafter, when the timer T 2  runs out of time, the main controller  1107 , in order to cut off the wireless link, transmits wireless-link disconnect request information ( 1518 ) to the extension wireless controller  1105   b . Upon receiving this information, the extension wireless controller  1105   b  transmits a disconnect request signal ( 1519 ) to the extension cordless telephone  1110   b.    
   Upon verifying completion of reception of the disconnect request signal ( 1519 ) at the extension cordless telephone  1110   b , the extension wireless controller  1105   b , as well as the extension cordless telephone  1110   b , halts the transmission of radio waves and cuts the wireless link. 
   When, during an outside-line call, a holding operation is performed at the extension cordless telephone  1110   a  in order to transfer or temporarily hold the call that is in progress, a hold signal is transmitted from the extension cordless telephone  1110   a  to the extension wireless controller  1105   a . Upon receiving this signal, the extension wireless controller  1105   a  transmits holding information to the main controller  1107 . 
   Upon receiving the holding information, the main controller  1107  sends a holding tone to the outside line and transmits outside-line holding information ( 1522 ,  1523 ) to the extension wireless controllers  1105   a ,  1105   b.    
   Upon receiving the outside-line holding information ( 1522 ) from the main controller  1107 , the extension wireless controller  1105   a  transmits an outside-line hold signal ( 1524 ) to the extension cordless telephone  1110   a  by the call channel since the wireless link has already been established. 
   Meanwhile, upon receiving the outside-line holding information ( 1523 ), the extension wireless controller  1105   b  transmits an outside-line hold signal ( 1525 ) to the extension cordless telephone  1110   b  by the control channel since a wireless link with the extension cordless telephone  1110   b  has not been established. 
   Upon receiving the outside-line hold signals ( 1524 ,  1525 ), the extension cordless telephones  1110   a ,  1110   b  light the outside-line LEDs in the patterns designated by the outside-line hold signals ( 1524 ,  1525 ). 
   Further, the holding operation of  FIG. 15  is performed after the wireless link between the extension wireless controller  1105   b  and extension cordless telephone  1110   b  is cut. However, if the holding operation is performed before the wireless link is cut, the transmission of the outside-line hold signal ( 1525 ) to the extension cordless telephone  1110   b  is performed by the call channel. 
   Thus, it is possible to answer an incoming call to an outside line and place the call in progress on hold. 
   Described next will be the sequence chart of  FIG. 16  showing operation when an outside-line button is pressed on the extension cordless telephone  1110   b  at such time that an outside line of the extension cordless telephone  1110   a  has been placed on hold, the sequence chart of  FIG. 17  showing operation when a response is made to the holding outside line at the extension cordless telephone  1110   b  in a state in which the timer T 2  is counting and a wireless link remains as established, and the flowchart of  FIG. 18  illustrating these operations. 
   When the outside-line button on the extension cordless telephone  1110   b  is pressed in order to respond to the holding outside line (step S 1801 ), the extension cordless telephone  1110   b  checks, using the wireless controller  1203 , whether the wireless link has been established (step S 1802 ). If the wireless link has been cut, the extension cordless telephone  1110   b  transmits a wireless-link establishment request signal ( 1601 ) to the extension wireless controller  1105   b  by the control channel in order to establish the wireless link (step S 1803 ). 
   Upon receiving the wireless-link establishment request signal ( 1601 ), the extension wireless controller  1105   b  transmits an establish request signal ( 1602 ) to the extension cordless telephone  1110   b  by the control channel, designates the call channel to be used and switches the receiving section, which receives radio waves from the extension cordless telephone  1110   b , over to the call channel, thereby establishing a wireless link. 
   Upon receiving the establish request signal ( 1602 ) at step S 1804 , the extension cordless telephone  1110   b  transmits a wireless-link establishment notification signal ( 1603 ) by the designated call channel (step S 1805 ). Upon receiving this signal, the extension wireless controller  1105   b  transmits a wireless-link establishment response signal ( 1604 ) to the extension cordless telephone  1110   b  by the call channel and transmits wireless-link establishment notification information ( 1605 ) to the main controller  1107 . 
   Upon verifying, owing to reception of the wireless-link establishment response signal ( 1604 ) from the extension wireless controller  1105   b  (step S 1806 ), that the wireless link has been established, the extension cordless telephone  1110   b  transmits an outside-line button signal ( 1606 ) to the extension wireless controller  1105   b  (step S 1807 ). Upon receiving this signal, the extension wireless controller  1105   b  sends the main controller  1107  information ( 1607 ) indicating depression of the outside-line button. 
   Upon receiving the information ( 1607 ), the main controller  1107  changes over the switching section  1103  and connects the call channel of the holding outside line from the extension wireless controller  1105   a  to the extension wireless controller  1105   b , thereby making possible an outside-line call at the extension cordless telephone  1110   b  (step S 1808 ). 
   If it is determined at step S 1802  that the wireless link has been established, a signal ( 1701 ) indicating depression of the outside-line button is transmitted to the extension wireless controller  1105   b  (step  1807 ) owing to the fact that the wireless link has been established. 
   Upon receiving the signal ( 1701 ), the extension wireless controller  1105   b  sends the main controller  1107  information ( 1702 ) indicating depression of the outside-line button. Upon receiving this information, the main controller  1107  changes over the switching section  1103 , connects the call channel of the holding outside line to the extension wireless controller  1105   b  and makes possible an outside-line call at the extension cordless telephone  1110   b  (step S 1808 ). 
   More specifically, if the established wireless link remains in effect when a transfer is made to another telephone or a hold response is made at another telephone after the response to the incoming call from the telephone line is made, the sending/receiving of signals at S 1803 ˜S 1806  described in  FIG. 18  and the sending/receiving of signals  1601 ˜ 1604  and sending/receiving of information  1605  in  FIG. 16  can be eliminated. The time required to hold and respond to an outside line and make a call possible can be shortened. 
   More specifically, as described in connection with  FIG. 14 , when the main unit detects an operation for responding to an incoming call, the time required to cut the wireless links between the main unit and extension cordless telephones other than that which performed the response operation is made longer than the time for cutting the wireless link by hanging up or by abandonment of the call on the originating side. As a result, the time needed for a hold response on the outside line can be shortened, as set forth above. 
   A fifth embodiment of the present invention will now be described. 
   In the fourth embodiment, it is so arranged that when an off-hook connection has been made on a wireless link, the set value of the disconnect timer of extension cordless telephones other than the extension cordless telephone that has answered is changed depending upon whether an outgoing call is abandoned by the originating side in mid-course or an operation is made to respond to an incoming call. In the fifth embodiment, it is so arranged that when an extension cordless telephone has performed an operation to respond to an incoming call, the wireless links to extension cordless telephones other than the extension cordless telephone that has responded are not cut. 
   Reference will be had to the flowchart of  FIG. 19  to describe an operation in which, when the main unit  1102  has detected an operation by the extension cordless telephone  1110   a  to respond to an incoming call, the wireless link of the extension cordless telephone  1110   b , which is other than the extension cordless telephone that responded, is not disconnected during acquisition of a telephone line. 
   In  FIG. 19 , steps S 1901 ˜S 1903  are the same as steps S 1401 ˜S 1403 , and steps S 1908 , S 1909  are the same as steps S 1408 , S 1409 . These steps need not be described again. 
   The operating status of the disconnect timer is checked at step S 1903 . If the timer is not operating, monitoring is performed (step S 1904 ) to determine whether the outside line responded to by the extension cordless telephone  1110   b  is continuing the call. If the call is continuing, the status, stored in the RAM  1109 , that prevailed when the wireless link was established is checked (step S 1905 ). In case of an off-hook connection, i.e., in case of disconnection owing to hanging up of the phone, the disconnect timer (e.g., 5 sec) is started (step S 1906 ). In case of an incoming-call connection, whether the incoming call was suspended is checked (step S 1907 ). If the call was abandoned from the originating side in mid-course, the program proceeds to step S 1906 , where the disconnect timer is started. The program then returns to step S 1901 . 
   If the call from the originating side is not abandoned at step S 1907  and the other dedicated extension cordless key telephone  1110   b  responds to the incoming call, the program returns to step S 1901  without starting the timer. 
   If the outside line responded to at step S 1904  has been disconnected, a procedure for cutting the wireless link is started (step S 1909 ) and the program makes a transition to step S 1910  to wait for completion of the wireless-link disconnection. 
   Thus, when the main unit  1102  has detected an operation for responding to an incoming call, the wireless links with all dedicated extension cordless telephones are not cut during acquisition of a telephone that has responded to an incoming call. When the telephone that has responded to an incoming call is disconnected, it is possible to cut the wireless links with all dedicated extension cordless telephones. 
     FIG. 20  is a diagram showing the construction of a system according to a sixth embodiment of the invention. 
   The system of  FIG. 20  is additionally provided with an extension wireless controller  1105   c  and a wireless facsimile device  1111 . The other components are the same as shown in  FIG. 11  and need not be described again. 
   The wireless facsimile device  1111  performs facsimile communication via the PSTN  1101 , and the extension wireless controller  1105   c  is for controlling the wireless facsimile device  1111 . The type (telephone, facsimile, etc.) of extension device connected to each extension wireless controller is stored in the RAM  1109  in advance. 
   In a case where a wireless data communication device such as the facsimile device in included in the system, as shown in  FIG. 20 , the probability that a transfer from the extension cordless telephones  1110   a ,  1110   b  will be made is low. Therefore, in this embodiment, the cutting of the wireless link of the wireless facsimile device  1111  is performed as in the fourth and fifth embodiments, namely at the time of off-hook connection or when an outgoing call is abandoned on the originating side. 
     FIG. 21  is a flowchart illustrating the operation of the main unit in this embodiment. Operation in accordance with this flowchart will now be described. 
   When a wireless link has been established between the extension wireless controller  1105  and the extension cordless telephones  1110  and wireless facsimile device  1111 , the main controller  1107  monitors the hook status of the extension cordless telephones  1110   a ,  1110   b  and wireless facsimile device  1111  (step S 2101 ). If any one of the extension cordless telephones  1110   a ,  1110   b  or wireless facsimile device  1111  is off the hook, the program returns to step S 2101 . If any one of these is on the hook, the main controller  1107  monitors the incoming-call status of the outside line (step S 2102 ). If the incoming call is continuing, the program returns to step  2101 . If there is no incoming call, the main controller  1107  checks a disconnect timer (step  2103 ). If the timer is not operating, the main controller  1107  checks the status, stored in the RAM  1109 , that prevailed when the wireless link was established (step S 2104 ). In case of an off-hook connection, the main controller  1107  starts the timer T 1  (step S 2105 ). In case of an incoming-call connection, the main controller  1107  checks whether the incoming call was suspended (step S 2106 ). 
   If the call was abandoned from the originating side in mid-course, the program proceeds to step S 2105 , where the disconnect timer T 1  is started. 
   If the call from the originating side is not abandoned at step S 2106 , an incoming-call response is made at step S 2107  after judging whether the wireless terminal is an extension cordless telephone or the wireless facsimile machine. If the wireless terminal is the facsimile device  1111 , the timer T 1  is started in order to cut the wireless link with the other wireless terminals (the extension cordless telephones  1110   a ,  110   b ). 
   If the extension cordless telephone has responded to the incoming call at step S 2107 , then the program proceeds to step S 2108 . 
   It is determined at step S 2108  whether the wireless link to be cut is that of the extension cordless telephones or of the wireless facsimile device. In case of the wireless facsimile device, the program proceeds to step S 2105 . If the wireless link cut is that of the extension cordless telephones, the disconnect timer T 2 , which has been set to a time longer than that of the disconnect timer T 1 , is started at step S 2109 . and the program returns to step S 1401 . 
   If the disconnect timer has already been started at step S 2103 , the timer performs a counting operation (step S 2110 ) and the program returns to step S 2101  if the timer has not run out of time. If the timer has run out of time, the timer is halted and a procedure for cutting the wireless link is started (step S 2111 ), after which the program makes a transition to step S 2112  to wait for completion of the wireless-link disconnection. 
   Thus, in a case where the system incorporates devices having various functions, the time up to cutting of the wireless link can be changed depending upon the communication function of the device. 
   In the fourth through sixth embodiments, the set time of the disconnect timer T 2  is longer than that of the disconnect timer T 1 . This set time is a fixed time period. However, in a seventh embodiment, it is so arranged that the set time of the disconnect timer T 2  can be changed by the operation in dependence upon application in which the system is put to use. 
     FIG. 22  is a diagram showing the construction of the main unit  1102  according to the seventh embodiment. 
   In  FIG. 22 , numeral  1112  denotes a control panel, which is provided with a switch of the kind shown in  FIG. 23 . This makes it possible to freely change the set time of the disconnect timer T 2 . Other components in  FIG. 22  are the same as those in  FIG. 20  and need not be described again. 
   In  FIG. 23 , numeral  2301  denotes a control panel having a display  2302  which displays the set time of the disconnect timer T 2 . By moving a variable switch  2303 , the time of the disconnect timer T 2  can be set with facility. 
   A control panel of this kind can be provided in the apparatus of the first through third embodiments, thereby making it possible to change the set values of the timers  250 ,  340 . 
   In the first through seventh embodiments, the example of the wireless link described relies upon radio waves from a low-power system. However, it is obvious that the present invention can be implemented in a similar manner also in various wireless telephone systems in which wireless communication relies upon very low-power radio waves or other radio waves, light such as infrared rays, etc. There is no particular limitation upon the type of wireless link. 
   The arrangement of the cordless key telephone apparatus shown in  FIG. 11  is only one example and it goes without saying that there are many other arrangements available. The invention is not limited to a key telephone apparatus. It is obvious that the invention is applicable in similar fashion to a cordless telephone system in a public branch exchange or business office. 
   With regard to the type of outside line, the invention is not limited to an ordinary public telephone line. The line may be an extension in a public branch exchange (PBX), a digital line typified by an ISDN, a special-purpose line or a line in a private network. 
   There is no limitation upon the type of extension terminal accommodated. If a plurality of dedicated cordless telephones are accommodated, dedicated telephones, ordinary subscriber telephones (SLTs), facsimile machines or other telephone terminals conventionally connected to the main unit by lines may be accommodated. 
   The extension wireless controllers are accommodated within the main unit. However, they may be provided outside the main unit and connected thereto by line wires. 
   In the foregoing embodiments, the timers in the main controller are described as being software. However, hardware timers may be employed. 
   In accordance with the embodiments of the invention described above, in an instance where a calling party receives a response from a party different from the intended party after the incoming call from a public telephone line is terminated and answered, as is often the case where a hold-and-transfer operation is used most frequently, the time needed for cutting of the wireless link after the response to an incoming call is made is lengthened. As a result, the operation for effecting transfer to another telephone or for holding and answering at another telephone can be facilitated and the waiting time of the calling party is shortened. 
   In a case where various devices, such as a facsimile device, which communicate data other than voice data are included in the system, the cutting of the wireless link can be performed in dependence upon the function of the device. 
   Further, by providing a switch for setting time up to the cutting of the wireless link, the operator is capable of setting the time in dependence upon the application or conditions of use. Accordingly, in a wireless communication system which accommodates devices having a plurality of functions, the time up to the cutting of the wireless link of each device can be changed in conformity with the function of the device and the state of use of the system. 
   As many apparently widely different embodiments of the present invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims.