Abstract:
Heretofore, depending on a network (switching device) to be used, call releasing has not been normally finished since a time until data link releasing took a value intrinsic to the device. According to the present invention, the counting of a predetermined time is started depending on determination as to the execution of call releasing. Then, depending on the passage of a predetermined time, the process of releasing a data link is started.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a communication device for carrying out the process of releasing a data link when a call is released, and a method and a program for controlling the communication device.  
           [0003]    2. Related Background Art  
           [0004]    In the D channel of an integrated services digital network (ISDN), a data link is set in its layer  2 , and a network layer is set in its layer  3 .  
           [0005]    In the control of the layers  3  and  2 , when calling or communications are finished, and a release-complete (REL-COMP) message is sent or received to release a call, the layer  3  makes a data link releasing request to the layer  2  by notifying Data Link (DL)-Release-Request, if no other currently used calls are present at a point of this time. Upon having received the DL-Release-Request, the layer  2  sends a disconnect (DISC) command as a data link cutting-off instruction to the network. After the reception of an unnumbered acknowledge (UA) response as a response to the command, the layer  2  outputs DL-Release-Confirmation to the layer  3 , thereby notifying the releasing of the data link.  
           [0006]    Upon having received the DISC command, an opposite communication side notifies DL-Release-Indication from the layer  2  to the layer  3  to release the data link, and sends the UA response to the network.  
           [0007]    In the conventional device, a time from the releasing of a call to the request of data link releasing made by the layer  3  to the layer  2  takes a value intrinsic to the device.  
           [0008]    However, depending on a network (switching device) to be used, if the DISK command of the layer  2  was sent without any proper time interval taken after the transmission or reception of the REL-COMP message of the layer  3 , the data link releasing process was not finished normally, bringing about the resetting of a data link by the network.  
           [0009]    Furthermore, since a permissible value for such a time interval varied from network to network (switching device), it was impossible to normally finish call releasing depending on a device installing place (switching device, to which the device was connected).  
         SUMMARY OF THE INVENTION  
         [0010]    It is an object of the present invention to enable a call to be released normally.  
           [0011]    It is another object of the invention to enable the execution of a data link releasing process suitable for a switching device, to which a communication device is connected. 
       
    
    
       [0012]    Other objects of the invention will become apparent from the following detailed description and drawings.  
       BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is a constitutional view of a communication device according to an embodiment of the present invention.  
         [0014]    [0014]FIG. 2 is a flowchart showing a process of the communication device of the embodiment.  
         [0015]    [0015]FIG. 3 is a flowchart showing a process of the communication device of the embodiment.  
         [0016]    [0016]FIG. 4 is a flowchart showing a process of the communication device of the embodiment.  
         [0017]    [0017]FIG. 5 is a flowchart showing a process of the communication device of the embodiment.  
         [0018]    [0018]FIG. 6 is a flowchart showing a process of the communication device of the embodiment.  
         [0019]    [0019]FIG. 7 is a sequential view during a data link releasing process of the embodiment.  
         [0020]    [0020]FIG. 8 is a sequential view during a data link releasing process of the embodiment.  
         [0021]    [0021]FIG. 9 is a sequential view when there is a calling request at a timer starting time according to the embodiment.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]    Next, the preferred embodiment of the present invention will be described with reference to the accompanying drawings.  
         [0023]    [0023]FIG. 1 is a block diagram showing the constitution of a communication device according to an embodiment of the invention.  
         [0024]    A CPU  101  is a system control unit in charge of control over the entire device. A ROM  102  stores a control program of the CPU  101 . A part of the control program for the CPU  101  is one for carrying out a process described below.  
         [0025]    A RAM  103  includes an SRAM, a DRAM or the like, and stores a program control variable or the like. The RAM  1 - 3  also stores a set value registered by a device user, management data of the device, and a buffer for various works.  
         [0026]    In addition, the RAM  103  stores a timer value of the described embodiment. The setting of the timer value is carried out by the device user through key entry from an operation display unit  106 . Setting information can be transferred from an external unit to the communication device through a predetermined interface, network or the like, and stored in the RAM  103 .  
         [0027]    An input unit  104  includes various input devices, e.g., a microphone, a scanner, and so on.  
         [0028]    An output unit  105  includes various output devices, e.g., a speaker, a printer, and so on.  
         [0029]    The operation display unit  106  includes a keyboard, a touch panel, an LCD, an LED or the like. This unit is used by the device user to perform various operations, and display notification is made to the device user.  
         [0030]    An ISDN I/F (interface) unit  107  controls transmission on D and B channels to carry out integrated services digital network (ISDN) communications through an ISDN line  108 .  
         [0031]    FIGS.  2  to  6  are flowcharts, each showing an example of the operation of the communication device of the embodiment.  
         [0032]    The operations shown in FIGS.  2  to  6  are performed by the CPU  101  based on programs stored in the ROM  102  or the RAM  103 , and each setting.  
         [0033]    [0033]FIG. 2 is a flowchart showing the operation at the time of call releasing.  
         [0034]    The CPU  101  determines the end of calling or communications, and the releasing of a call in S 201 , and then checks on whether a data link is released or not in S 202  (details are described later). If it is determined in S 203  that the result of the checking in S 202  indicates releasing, then the process proceeds to S 204 . If the result of the checking in S 202  indicates otherwise, the process is finished.  
         [0035]    Then, in S 204 , a timer value preset by the key entry of the operation display unit  106  and stored in the RAM  103  is read. As described above, the timer value may be one that has been transferred from the external unit, and stored in the RAM  103 . If it is determined in S 205  that the timer value is 0, in S 207 , Data Link (DL)-Release-Request is notified from the layer  3  to the layer  2  to request the releasing of the data link, and a current state is placed on standby for link releasing. Then, in S 209 , a disconnect (DISC) command is sent to the network. If it is determined in S 205  that the timer value is not 0, in S 206 , the timer of the value read in S 204  is started.  
         [0036]    [0036]FIG. 3 is a flowchart showing the operation at the time of completion of the timer started in S 206  shown in FIG. 2.  
         [0037]    After having determined in S 301  that the timer has been completed, in S 302 , the CPU  101  notifies DL-Release-Request from the layer  3  to the layer  2  to request the releasing of the data link. Then, in S 303 , a current state is placed on standby for link releasing. In S 304 , a DISC command is sent to the network.  
         [0038]    [0038]FIG. 4 is a flowchart showing the operation at the time of call generation.  
         [0039]    After having determined in S 401  that a new call has been generated, in S 402 , the CPU  101  determines whether the timer started in S 206  of FIG. 2 is in operation or not. If the on-going operation of the timer is determine in S 402 , the timer is stopped in S 403 , and normal processing at the time of call generation, i.e., processing such as SETUP transmission, or the like for generating a call, is carried out in S 404 . If the on-going operation of the timer is not determined in S 402 , then normal processing at the time of call generation is executed in S 404 .  
         [0040]    [0040]FIG. 5 is a flowchart showing the operation at the time of receiving data link releasing notification.  
         [0041]    In S 501 , the CPU  101  receives a DISC command from the network. Upon having determined that DL-Release-Request has been notified from the layer  3  to the layer  2 , and data link releasing notification has been received, in S 502 , the CPU  101  determines whether the timer is in operation or not. If the on-going operation of the timer is determined in S 502 , the timer is stopped in S 503  and, in S 504 , normal processing at the time of receiving the data link releasing notification, i.e., processing such as transmission of unnumbered acknowledge (UA) response to the network or the like, is carried out. If the on-going operation of the timer is not determined in S 502 , then normal processing at the time of receiving the data link releasing notification is executed in S 504 .  
         [0042]    [0042]FIG. 6 is a flowchart showing checking on whether the data link is released or not (processing of S 202  in FIG. 2).  
         [0043]    If it is determined in S 601  that a current state is not link connecting setting, it can be understood that the data link has already been set. Accordingly, in S 605 , non-releasing of the data link is set as the result of the checking.  
         [0044]    If it is determined in S 602  that there is another call using the line, similarly, non-releasing of the data link is set as the result of the checking in S 605 .  
         [0045]    Similarly, if it is determined in S 603  that the terminal is not set for releasing the data link (permanent link setting), in S 605 , non-releasing of the data link is set as the result of the checking.  
         [0046]    Only when it is determined in S 601  that a current state is link connection setting, it is determined in S 602  that no other calls are present using the line, and it is determined in S 603  that setting is not permanent link setting, in S 604 , releasing of the data link is set as the result of the checking.  
         [0047]    [0047]FIG. 7 is a view showing an example of a normal sequence of data link releasing. When a call is released by the transmission of a release complete (REL-COMP) message, the determination operations of S 601 , S 602  and S 603  in FIG. 6 are executed. If the releasing of the data link is determined as a result, the timer is started. After the completion of the timer, based on the DL-Release-Request from the layer  3 , the DISC command is transmitted from the layer  2  to the network. After the reception of the UA response from the network, DL-Release-Conformation is sent to the layer  3  to notify the releasing of the data link.  
         [0048]    [0048]FIG. 8 is a view showing an example of a sequence when data link releasing notification is received during the operation of the timer. When the DISC command is received from the network during the operation of the timer, the UA response is sent from the layer  2  to the network. Then, DL-Release-Indication is sent from the layer  2  to the layer  3  to notify the releasing of the data link. After the reception of the data link releasing notification, at the layer  3 , the timer is stopped because of the ongoing operation of the timer.  
         [0049]    [0049]FIG. 9 is a view showing an example of a sequence when a calling request is made during the operation of the timer. When calling is requested during the operation of the timer, at the layer  3 , calling is carried out based on a SETUP message. At this time, since the timer is in operation, the timer is stopped.  
         [0050]    The foregoing operations are carried out by the CPU  101  based on the programs stored in the ROM  102 , the RAM  103 , and so on. However, such programs may be stored in various external storage media, e.g., a floppy disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a memory card, and so on, and executed by the CPU  101 .  
         [0051]    As can be understood from the foregoing, according to the invention, it is possible to carry out a data link releasing process suitable for the switching device, to which the communication device is connected.