Abstract:
A base station has a wireless communication unit for wirelessly communicating with a wireless terminal; means for connecting to and disconnecting from a wireless network; a storage unit for storing service area information defining a service area around the base station, the wireless terminal located inside the service area being allowed to connect to the network via the wireless communication unit of the base station; a measuring unit for measuring the location of a wireless terminal; first determining means for determining whether a wireless terminal is located in the service area around the base station on the basis of the location of the wireless terminal measured by the measuring unit; connecting means for connecting a wireless terminal to the network via the base station in a case that the wireless terminal is determined by the first determining means to be located in the service area around the base station; monitoring means for monitoring the location of the wireless terminal which is connected to the network by the connecting means; second determining means for determining whether the wireless terminal monitored by the monitoring means is located inside the service area; and means for disconnecting a connection from a wireless terminal to the network via the wireless communication unit of the base station in a case that the wireless terminal is determined by the second determining means to be located outside the service area.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a method and an apparatus for connecting to and disconnecting from a wireless network.  
         [0003]     2. Description of the Related Art  
         [0004]     Recently, it has become increasingly common to use electronic meeting systems where wireless terminals are installed in meeting rooms or the like.  
         [0005]     A patent publication JP 2003-A-085112 discloses an example of such an electronic meeting system. The electronic meeting system includes a local area network (LAN), a wireless terminal(s), an access point (this will be referred as ‘AP’), and a projector connected to the LAN. The AP provides a wireless terminal with a wireless connection to the LAN.  
         [0006]     When a meeting is held in a meeting room, a person (s/he will be referred to as an ‘attendee’) may carry a wireless terminal storing data for a presentation. The attendee accesses the LAN via the AP to join the electronic meeting system to make their presentation. The data is then transferred from the wireless terminal to the projector via the LAN, and the presentation data is projected onto the screen by the projector. The attendee may also access other available resources on the LAN. When accessing the electronic meeting system, the attendee is required to input a password. When leaving the meeting room, the attendee is required to disconnect manually from the LAN so as to withdraw from the electronic meeting system.  
         [0007]     A patent publication JP 2003-A-333559 discloses another example of such an electronic meeting system. The electronic meeting system also includes a LAN, a host computer, an AP, a wireless terminal(s), and a projector connected to the LAN. Similarly to the first example, an attendee is required to input a password to access an electronic meeting system from a wireless terminal such as a PC (Personal Computer). In this example, the host computer generates a meeting-specific password for each meeting, and displays the generated password on a screen by controlling the projector. The attendee inputs the displayed password. Once the password is input, the attendee can access the electronic meeting system from their wireless terminal to exchange data relating to the meeting with other stations.  
         [0008]     In both of the foregoing examples, it may be possible to access the electronic meeting system from outside a meeting room via the AP, since the radio signals tend to diminish gradually as a distance from the meeting room increases. Accordingly, an attendee may be able to access the electronic meeting system even after leaving the meeting room.  
         [0009]     Furthermore, an attendee of a meeting may remain in a region outside the meeting room, after leaving the meeting room and intentionally leaving their PC connected to the electronic meeting system. The attendee may then intercept information exchanged via the electronic meeting system. For example, after attending a board meeting held in a meeting room to explain a proposal using the electronic meeting system, an employee is able to intercept confidential information in the board meeting from a region outside the meeting room.  
       SUMMARY OF THE INVENTION  
       [0010]     The present invention has been made in view of the above circumstances and provides a method and apparatus for connecting to and disconnecting from a wireless network.  
         [0011]     According to an aspect of the present invention, the base station has 
        a wireless communication unit for wirelessly communicating with a wireless terminal; means for connecting to disconnecting from a network; a storage unit for storing service area information defining a service area around the base station, the wireless terminal located inside the service area being allowed to connect to the network via the wireless communication unit of the base station; a measuring unit for measuring the location of a wireless terminal; first determining means for determining whether a wireless terminal is located in the service area around the base station on the basis of the location of the wireless terminal measured by the measuring unit; connecting means for connecting a wireless terminal to the network via the base station in a case that the wireless terminal is determined by the first determining means to be located in the service area around the base station; monitoring means for monitoring the location of the wireless terminal which is connected to the network by the connecting means; second determining means for determining whether the wireless terminal monitored by the monitoring means is located inside the service area; and means for disconnecting a connection from a wireless terminal to the network via the wireless communication unit of the base station in a case that the wireless terminal is determined by the second determining means to be located outside the service area.        
 
         [0013]     According to an aspect of the present invention, a wireless communication network has the base station described above.  
         [0014]     Accordingly, the base station connects a wireless terminal to a network via the base station only in a case that the wireless terminal is located in the service area. Thus, in an exemplary case that the service area is set inside a meeting room, after an attendee leaves the meeting room carrying their wireless terminal, they can no longer use the wireless terminal to access information exchanged in the meeting held in the meeting room.  
         [0015]     According to an aspect of the present invention, the base station further has means for setting-up transmitting characteristics of the wireless communication unit of the base station on the basis of the service area information stored in the storage unit. Accordingly, the transmitting characteristics including transmitting power may be set-up on the basis of shape and size of a service area and the location of a base station in the service area. Thus an area covered by radio signals transmitted from a base station may be kept as small as possible while still enabling communication with wireless terminals in the service area around the base station. Namely, a spillover area outside the service area may be kept as small as possible.  
         [0016]     According to an aspect of the present invention, the wireless communication unit of the base station transmits a message to a wireless terminal in accordance with the transmitting characteristics set up by the setting-up means, and the measuring unit of the base station measures the location of a wireless terminal only in a case of receiving a response to the message from the wireless terminal within a predetermined time.  
         [0017]     According to an aspect of the present invention, the method is performed by a base station and has the steps of: measuring a location of a wireless terminal; first determining whether a wireless terminal is located in a service area of the base station on the basis of the location of the wireless terminal measured in the measuring step; 
        connecting a wireless terminal to a network via the base station in a case that the wireless terminal is determined to be located in the service area in the first determining step;     monitoring the location of the wireless terminal connected to the network in the connection step;     second determining whether a wireless terminal is located in the service area of the base station on the basis of the location of the wireless terminal monitored in the monitoring step;     disconnecting a connection from a wireless terminal to the network via the base station in a case that the wireless terminal is determined to be located outside the service area in the second determining step.        
 
         [0022]     According to an aspect of the present invention, a computer program product enables a computer of a base station to perform the processes of: measuring a location of a wireless terminal; first determining whether a wireless terminal is located in a service area of the base station on the basis of the location of the wireless terminal measured in the measuring process; connecting a wireless terminal to a network via the base station in a case that the wireless terminal is determined to be located in the service area in the first determining process; monitoring the location of the wireless terminal connected in the connecting process; second determining whether a wireless terminal is located in the service area of the base station on the basis of the location of the wireless terminal monitored in the monitoring process; disconnecting a connection from a wireless terminal to the network via the base station in a case that the wireless terminal is determined to be located outside the service area in the second determining process.  
         [0023]     According to an aspect of the present invention, the above computer program product is stored in the computer-readable storage medium. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]      FIG. 1  illustrates an overview of a communication system according to an embodiment of the present invention.  
         [0025]      FIG. 2  is a functional block diagram of Access Point (AP)  40 .  
         [0026]      FIG. 3  illustrates a structure of antenna  405   a.    
         [0027]      FIG. 4  illustrates radio wave emission characteristics of antenna  405   a.    
         [0028]      FIG. 5  illustrates template data  406   a , each indicating a shape of a meeting room.  
         [0029]      FIG. 6  illustrates location map  406   b.    
         [0030]      FIG. 7  illustrates management table  406   c.    
         [0031]      FIG. 8  illustrates relations between reception levels of radio signals at wireless terminal  60  and distances from wireless terminals.  
         [0032]      FIGS. 9 and 10  are flowcharts illustrating operations of AP 40 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0033]     Details of the present invention will be described with reference to the attached drawings.  
       A. Configuration  
       [0034]      FIG. 1  illustrates an overview of a communication system according to an embodiment of the present invention.  
         [0035]     In the present embodiment, LAN  70  includes an access point  40  (this will also be referred as “AP 40 ”), wireless terminals  60   a - 60   c  located in meeting room  10 , a host computer  50 , and a network connectable projector  30 , as illustrated in  FIG. 1 .  
         [0036]     As illustrated in  FIG. 1 , an access point  40  is situated in a meeting room  10 . A plurality of access points  40  may be placed in meeting room  10 . Access point  40  provides wireless terminal  60   a - 60   c  located in meeting room  10  with a wireless connection to LAN  70 .  
         [0037]     A projector  30  and a screen  20  for projecting images thereon are also placed in meeting room  10 . As illustrated in  FIG. 1 , projector  30  is connected to AP 40  with a cable. Projector  30  may also be connected to AP 40  wirelessly.  
         [0038]     Host computer  50  is detachably connected to LAN 70 , and provides a function of setting parameters in AP 40 .  
         [0039]     Although the communication system is installed in meeting room  10  in the example illustrated in  FIG. 1 , the present communication system may be installed throughout a whole floor of a building, an entire building, or the like.  
         [0040]     Wireless terminal  60   a - 60   d  will be simply referred as “wireless terminal  60 ” later, where no distinction is required.  
         [0041]     Wireless terminal  60  is configured, for example, as a notebook type personal computer equipped with a wireless LAN interface card, and may store presentation data including image and document data. Wireless terminal  60  may be configured as a PDA (Personal Digital Assistant) having a wireless communication function or as a mobile phone accommodated in a base station of a mobile communication system.  
         [0042]     The presentation data, stored in the wireless terminal  60  carried into meeting room  10  by an attendee, may be transferred to projector  30  for presentation, when the wireless terminal  60  is connected to LAN 70  via AP 40 . The attendee may exchange data via LAN 70  with wireless terminals of other attendees.  
         [0043]      FIG. 2  illustrates a functional block diagram of AP 40 .  
         [0044]     CPU 401  executes computer programs stored in ROM 402  and/or hard disk drive HD 406  so as to control AP 40 . ROM 402  stores programs and data for controlling AP 40 . RAM 403  is used as a working area of CPU 401 . Communication interface  404  handles communications with projector  30 .  
         [0045]     Wireless communication unit  405  has an antenna  405   a  and a high-frequency transmission/reception circuit including an amplifier(s) and a frequency converter(s), and handles wireless communications with wireless terminal  60 .  
         [0046]     Antenna  405   a  includes, as illustrated in  FIG. 3 , a vertical monopole antenna element  451  disposed in a center, and six parasitic antenna elements  452  disposed around vertical monopole antenna element  451  at 60 degree intervals. The antenna may be an ESPA antenna (Electronically Steerable Parasitic Array Radiator Antenna) developed by Wave Engineering Laboratories.  
         [0047]     Vertical monopole antenna element  451  is directly connected to the high-frequency transmission/reception circuit of wireless communication unit  405 , whereas each parasitic antenna element  452  is grounded via a resistive element such as a variable capacitance diode. According to the configuration, antenna  405   a  requires only one high-frequency transmission/reception circuit. Thus, the construction cost and the power consumption of AP 40  may be reduced in comparison to other configurations such as active phased array antenna.  
         [0048]     Wireless communication unit  405  may change electromagnetic coupling between vertical monopole antenna element  451  and each parasitic antenna element  452  by changing resistances of the resistive element connected to each parasitic antenna elements  452 , so as to change the propagation direction and pattern of a radio wave emitted from antenna  405   a.    
         [0049]     For example, wireless communication unit  405  may change the propagating direction of a radio wave emitted from antenna  405   a  at 60 degree intervals as illustrated in  FIG. 4 , and control the transmission power so that the radio wave might propagate a prescribed distance in the direction.  
         [0050]     Details of antenna  405   a  are described, for example in “Scanning Electron Guide Array Antenna”, by Takashi Ohira, et. al. in IEICE Journal J87-C, 1, pp. 12-31, 2004-01.  
         [0051]     The configuration of antenna  405   a  may be modified, for example, in the number of parasitic antenna elements  452 , and is not limited to the example illustrated in  FIG. 3 . For example eight parasitic antenna elements  452  may be disposed around vertical monopole antenna element  451  at 45 degree intervals, or twelve parasitic antenna elements  452  may be disposed around vertical monopole antenna element  451  at 30 degree intervals.  
         [0052]     HD 406  stores a SSID (Service Set Identifier) assigned to each AP 40 , a meeting-specific password for each meeting, and identification information of one or a plurality of wireless terminal(s)  60 . Identification information of wireless terminal  60  is uniquely assigned to each wireless terminal  60  to identify it in LAN 70  and includes a MAC address or a nickname.  
         [0053]     HD 406  stores a plurality of template data  406   a  as illustrated in  FIG. 5 , data of each template indicating a shape of a service area, inside which wireless terminal  60  may connect to LAN 70  via AP 40 . In the present embodiment, data of each template defines an outline of meeting room  10 .  
         [0054]     HD 406  stores location map  406   b  and management table  406   c , both of which are used to manage locations of wireless terminals  60  which are located inside meeting room  10  and connected to LAN 70  via AP 40 .  
         [0055]     In location map  406   b , current locations of wireless terminals  60  are plotted relative to direction and distance from the installed location of AP 40  in meeting room  10 , as illustrated in  FIG. 6 .  
         [0056]     As illustrated in  FIG. 7 , management table  406   c  stores a MAC address as identification information of wireless terminal  60  connected to LAN 70  via AP 40 , and the tag code dynamically assigned to the identification information of wireless terminal  60 .  
       B. Operations  
     Preparing Service Area Information  
       [0057]     In the present embodiment, service area information is prepared as follows:  
         [0058]     When switched on, host computer  50  receives a plurality of template data  406   a  from AP 40 , and displays the received plurality of template data  406   a  on its display.  
         [0059]     A meeting room administrator operates host computer  50  to select as a shape of service area an appropriate template data  406   a  which best fits the outline shape of meeting room  10 . If no template data  406   a  fit the outline shape of meeting room  10 , the person may operate host computer  50  to generate data indicating a shape of a service area, and store it as new template data.  
         [0060]     After selecting or generating data indicating a shape of a service area, the administrator operates host computer  50  to input numerical data indicating a size of a service area. For example, when meeting room  10  is square and has 10 meter sides, the administrator inputs numerical data “10 m” indicating the length of the side.  
         [0061]     The administrator operates host computer  50  to define the location of AP 40  in the service area, namely, in meeting room  10 , in the present embodiment.  
         [0062]     Then, service area information, including the shape of the service area, numerical data indicating the size of the service area, and information on the location of AP 40  in the service area is transmitted from host computer  50  to AP 40 , and stored in HD 406  of AP 40 .  
       Calculation of Transmission Power  
       [0063]     On receiving from host computer  50  information on the shape and size of meeting room  10  and the information on the location of AP 40  in meeting room  10 , AP 40  calculates a transmission power pattern of antenna  405   a , the calculation being used to determine transmission power required for each direction to communicate with wireless terminals  60  located in meeting room  10 , and stores the calculated transmission power pattern in HD 406 . More specifically, AP 40  calculates a minimum transmission power for each direction required to steadily communicate with any wireless terminal  60  located in meeting room  10 . In the present embodiment, the transmission power pattern is represented as two-dimensional. However, a three-dimensional transmission power pattern may be employed in a case where it is necessary to take into account a three-dimensional shape of a meeting room.  
         [0064]     AP 40  communicates with wireless terminal  60  located in meeting room  10  by using the transmission power required for the direction in which wireless terminal  60  is located, in accordance with the calculated transmission power pattern.  
         [0065]     Accordingly, AP 40  may communicate steadily with wireless terminal  60  located in meeting room  10 , while AP 40  may shorten a propagating distance of radio signals so that the radio signal overspill region outside meeting room  10  may be reduced. Namely, a surrounding area of meeting room  10 , where the radio wave may be received, is reduced. Thus, security risks, such as theft of data transmitted from AP 40  to wireless terminal  60 , may be reduced.  
         [0066]     AP 40  may store in HD 406  another transmission power pattern dedicated for measurement of current locations of wireless terminals  60 .  
       Measurement of Location of Wireless Terminal  60   
       [0067]     AP 40  broadcasts radio signals for measuring current locations of wireless terminals  60  in accordance with the transmission power pattern which is stored in HD 406  for this measurement.  
         [0068]     On receiving the broadcasted signal, wireless terminal  60  measures reception level Pr for the received signal, and transmits to AP 40  a message including the measured reception level Pr.  
         [0069]     On receiving the message from wireless terminal  60 , AP 40  determines the direction from AP 40  to wireless terminal  60  on the basis of the most receive-sensitive direction of antenna  405   a  at the time of the reception, and calculates the distance from AP 40  to wireless terminal  60  on the basis of the reception level Pr included in the received message and the transmission power of the broadcast signal in the determined direction. Thus, AP 40  measures a location of wireless terminal  60 .  
         [0070]     Specifically, distance d from AP 40  to wireless terminal  60  may be approximately calculated from reception level Pr at wireless terminal  60 , and transmission power Pt at AP 40 , in accordance with equation (1). 
 
 Pr=Pt−Lp+Gt+Gr   (1), 
 
 where Pr (dBm) is reception level at wireless terminal  60 ; Pt (dBm) is transmission power at AP 40 ; Lp (dB) is loss in propagation; Gt (dBi) is transmission antenna gain at AP 40 ; and Gr (dBi) is reception antenna gain at wireless terminal  60 . In the present embodiment, LP may be practically approximated with Lb (fundamental propagation loss in a free space), which represents Lp in the case of an anisotropic antenna with zero gain. Lb is derived in accordance with equation (2). 
 
 Lb= 20 log 10 (4 πdf/ 3×10 8 )  (2), 
 
 where d (m) is distance from AP 40  to wireless terminal  60 ; and f (Hz) is a frequency of radio signals. 
 
         [0071]     The calculated distance d is correct only in an ideal case where no propagation loss arises. The propagation loss includes reflection of a radio wave from the surfaces of surrounding walls.  
         [0072]      FIG. 8  illustrates relations between reception level Pr (dBm) at wireless terminal  60  and distance d(m) from AP 40  to wireless terminal  60 , in a case that f is set at either 2.4 GHz or 5.0 GHz, Pt is set at 10 dBm, Gt is set at 2.2 dB, and Gr is set at 2.2 dBi. In a real situation where various propagation losses occur including reflections of radio wave, reception level Pr of wireless terminal  60  becomes smaller than the value shown in  FIG. 8 . In the following example, Pr, Gt, Gr are set to 10, 2.2, 2.2, respectively, in equation (1).  
         [0073]     More specifically, CPU 401  reads the transmission power pattern stored in HD 406 , generates a command message for instructing the transmission of a signal for measuring a location of wireless terminal  60  by including the transmission power pattern, and transmits the command message to wireless communication unit  405 .  
         [0074]     When receiving the command message, wireless communication unit  405  controls the transmission power and emission direction of radio signals from antenna  405   a  in accordance with the transmission power pattern included in the received command message. Accordingly, radio signals for measuring current locations of wireless terminals  60  propagate from antenna  405   a  within a prescribed area around the prescribed directions set by 60 degree intervals as illustrated in  FIG. 4 .  
         [0075]     On receiving via wireless communication unit  405  a terminal reception message including reception level at wireless terminal  60  of the signal for measuring a location, CPU 401  determines direction and calculates distance of wireless terminal  60  relative to AP 40  on the basis of the reception level included in the terminal reception message and the transmission power and transmission direction of the signal for measuring the location. Thus, a current location of wireless terminal  60  is measured.  
         [0076]     A similarly constructed antenna to the antenna  405   a  may be applied for other known methods of measuring the location of wireless terminal  60 .  
         [0077]     AP 40  may also calculate the transmission power of wireless terminal  60  by taking account of the location of wireless terminal  60  in meeting room  10  and antenna characteristics of wireless terminal  60 , and notify the calculated transmission power to wireless terminal  60 . Then, wireless terminal  60  transmits radio signals with the notified transmission power. According to this modification, the spillover of the signals transmitted from wireless terminal  60  outside meeting room  10  may be reduced.  
         [0078]     Furthermore, host computer  50  may pre-store transmission power calculated for AP 40  or wireless terminal  60  and notify them to AP 40  or wireless terminal  60 , respectively.  
       Initial Connection to LAN 70   
       [0079]      FIG. 9  is a flowchart illustrating operations of AP 40  when wireless terminal  60  requests AP 40  to connect to LAN 70 . In the present embodiment, AP 40  pre-stores in HD 406  a meeting-specific password for each meeting and MAC addresses (or nicknames) of wireless terminals  60  which are entitled to join each meeting.  
         [0080]     As illustrated in  FIG. 9 , on receiving a connection request to LAN 70  from wireless terminal  60  (Step S 101 ), AP 40  compares the SSID, password, nickname and MAC address included in the request and the corresponding entity stored in HD 406 , so as to authenticate wireless terminal  60  (Step S 102 ). In the present example, wireless terminal  60  is not authenticated when nickname, MAC Address or password included in the received connection request differ from the corresponding entity stored in HD 406 .  
         [0081]     When wireless terminal  60  is not authenticated (Step S 103 :NO), AP 40  transmits to wireless terminal  60  a message indicating that connection to LAN 70  is prohibited (Step S 104 ), and terminates the operations illustrated in  FIG. 9 .  
         [0082]     When wireless terminal  60  is authenticated (Step S 103 :YES), AP 40  measures a location of wireless terminal  60  (Step S 105 ), and plots the currently measured location of wireless terminal  60  in location map  406   b  (Step S 106 ).  
         [0083]     AP 40  determines whether wireless terminal  60  is located in meeting room  10  by taking account of service area information stored in HD 406  (shape and size of meeting room  10 , the location of AP 40  in meeting room  10 ) (Step S 107 ).  
         [0084]     In a case of determining that wireless terminal  60  is located outside meeting room  10  (Step S 107 :NO), AP 40  transmits to wireless terminal  60  a message indicating that a connection to LAN 70  is prohibited (Step S 104 ), and terminates the operations illustrated in  FIG. 9  without connecting to LAN 70 .  
         [0085]     In a case of determining that wireless terminal  60  is located in meeting room  10  (Step S 107 :YES), AP 40  assigns the wireless terminal  60  a new tag code (Step S 108 ), and stores the newly assigned tag code in management table  406   c  corresponding to the identification information unique to the wireless terminal (Step S 109 ), and transmits the newly assigned tag code to wireless terminal  60  (Step S 110 ). In the present example, a MAC address is used as identification information.  
         [0086]     Thus, wireless terminal  60  connects to LAN 70  via AP 40 .  
       Operations after Initial Connection to LAN 70   
       [0087]      FIG. 10  is a flowchart illustrating operations of AP 40  after initial connection to LAN 70 . AP 40  monitors whether wireless terminal  60  connected to LAN 70  via AP 40  is located inside/outside meeting room  10 .  
         [0088]     Specifically, CPU 401  of AP 40  performs the operations illustrated in  FIG. 10  periodically; for example, every three seconds.  
         [0089]     As illustrated in  FIG. 10 , AP 40  measures current locations of all wireless terminals  60  registered in management table  406   c  (Step S 201 ). AP 40  updates locations of wireless terminals  60  stored in location map  406   b  with the current locations of wireless terminals  60 (Step S 202 ).  
         [0090]     AP 40  determines whether each wireless terminal  60  is located inside or outside meeting room  10  by using service area information, such as the shape or the size of meeting room  10 , or the location of AP 40  within meeting room  10  (Step S 203 ).  
         [0091]     When determining that wireless terminal  60  is located inside meeting room  10  (Step S 203 :YES), AP 40  transmits to wireless terminal  60  a request of notification, which requests wireless terminal  60  to transmit AP 40  identification information and a tag code assigned to the wireless terminal  60 (Step S 204 ). When receiving from wireless terminal  60  the identification information and the tag code within a prescribed time (Step S 205 :YES), AP 40  compares the received tag code and the tag code stored in management table  406   c  corresponding to the identification information of the wireless terminal  60 (Step S 206 ).  
         [0092]     When the received tag code agrees with the stored one (Step S 206 :YES), AP 40  assigns a new tag code to the wireless terminal  60 , stores the new tag code in management table  406   c  corresponding to the identification information of wireless terminal  60  (Step S 207 ), and transmits the new tag code to the wireless terminal  60  (Step S 208 ). In the present example, a MAC address is used for identification information of wireless terminal  60 .  
         [0093]     Furthermore, the new tag code may be scrambled before it is transmitted to wireless terminal  60  in Step S 208 . According to this modification, a connection to LAN 70  from a wireless terminal  60  which transmits false identification information may be disconnected.  
         [0094]     When determining that wireless terminal  60  is located outside meeting room  10  (Step S 203 :NO), a message of compulsory disconnection is transmitted to wireless terminal  60 (Step S 209 ), and the record of wireless terminal  60  is deleted from management table  406   c (Step S 210 ).  
         [0095]     Thus, the connection to LAN 70  from wireless terminal  60  via AP 40  is disconnected, when wireless terminal  60  moves out of meeting room  10 .  
       Closing Operations  
       [0096]     At the end of a meeting, AP 40  receives from host computer  50  a notification that the meeting has ended.  
         [0097]     On receiving the notification, AP 40  transmits to all wireless terminals  60  registered in management table  406   c  a message notifying compulsory disconnection, and deletes records of all wireless terminals  60  from management table  406   c.    
         [0098]     AP 40  may receive the notification of the end of the meeting from a specific wireless terminal  60 ; for example, that which the chairperson of the meeting is using.  
       C. Modifications  
       [0099]     (1) When receiving a connection request from wireless terminal  60  at Step S 102 , AP 40  may determine whether the wireless terminal  60  is located in the vicinity of meeting room  10  and authenticate the wireless terminal  60  at Step S 103  and subsequent steps. Specifically, AP 40  transmits a request for an acknowledgement message to a wireless terminal  60 , while controlling the coverage area of radio wave. AP 40  determines whether it has received an acknowledgement message from wireless terminal  60  within a prescribed time. Only in a case of receiving the acknowledgement message within the prescribed time, AP 40  executes the process at Step S 103  and subsequent steps. Accordingly, AP 40  need not execute the process at Step S 103  and subsequent steps of handling an unintentional connection request from wireless terminals located outside meeting room  10 .  
         [0100]     (2) AP 40  may disconnect from a wireless terminal  60  to LAN 70 , only in a case of determining multiple successive times that the wireless terminal  60  is located outside meeting room  10 . Namely, AP 40  may disconnect the connection from a wireless terminal  60  to LAN 70 , only in a case of determining that the wireless terminal  60  is located for longer than a prescribed time (for example, 10 seconds) outside meeting room  10 . Accordingly, disconnections due to misrecognition that wireless terminal  60  is located outside meeting room  10  may be reduced. Such misrecognition may be caused by, for example, noise interference.  
         [0101]     (3) Longitude/latitude information may be used when defining a service area. Furthermore, in a case that AP 40  has a GPS (Global Position Sensing) receiving unit, the location of AP 40  in service area may be automatically defined on the basis of the absolute location of AP 40  measured by the GPS receiving unit.  
         [0102]     (4) The computer program may be downloaded from a network and installed in a computer to cause the computer to execute the processes according to the present invention. The computer program may be stored and distributed in any computer-readable media.