hereinafter , the present invention will be described in further detail with reference to the accompanying drawings . the preferred embodiments of the present invention are illustrated in the drawings . however , the present invention can be carried out in various different modes and should not be read as being limited to the embodiments described in this specification . the embodiments are rather given to render the disclosure of the specification comprehensive and complete so that those skilled in the art fully understand the scope of the present invention . first , the schema of a wireless lan ( local area network ) system in an embodiment of the present invention will be described . fig1 is a view for explaining a wireless lan system in an embodiment of the present invention . referring to fig1 , in the wireless lan system , a plurality of access points ( in a strict sense , communication control devices , each constituting an access point ) ap 1 and ap 2 are logically connected in cascade arrangement to a wired network ( a wired nw ) constituted by a wired lan . a wireless channel ( a wireless line ) ch 6 is used in a wireless or radio zone ( a wireless lan zone or a service area ) rz 1 under the control of the access point ap 1 , whereas a wireless channel ch 1 is used in a wireless zone rz 2 under the control of the access point ap 2 . each of the access points ap 1 and ap 2 and terminals ( wireless lan terminals or mobile terminals ) 1 , 2 and 3 operates with a wireless frequency signal assigned to it . herein , the terminal 1 in the wireless zone rz 1 under the control of the access point ap 1 ( hereinafter , also referred to as the terminal under the control of the access point ) moves into the wireless zone rz 2 under the control of the access point ap 2 . in the wireless zone rz 2 under the control of the access point ap 2 , the plurality of terminals 2 and 3 are already present to perform data communication with the access point ap 2 . fig1 shows a frame ( a terminal movement notification frame ) for advance notification of movement of a terminal performing transmission from the access point ap 1 to the access point ap 2 through the wired nw when the terminal , which is preregistered at the access point ap 1 as being capable of performing priority data transmission , moves in the wireless lan system shown in fig1 . in the case where a priority bit in ip ( internet protocol ) data ( movement information ) in a data field df of the terminal movement notification frame received at the access point ap 2 is a “ 1 ” ( priority ) state , the access point ap 2 transmits a frame for instructing the terminals 2 and 3 under its control to wait for transmission ( a transmission standby frame ) so that the priority is given to the data transmission of the terminal 1 corresponding to a mobile terminal mac address described in the data field df in the frame . fig1 shows an example of the transmission standby frame transmitted from the access point ap 2 to the terminals 2 and 3 under its control . the terminals 2 and 3 under the control of the access point ap 2 , which receive the transmission standby frame with the standby instruction bit in the data field df being “ 1 ”, stop the data transmission . after transmitting data to the access point ap 2 , the terminal 1 moving thereto transmits a data transmission completion notification . fig1 shows a transmission standby timer table provided in the access point ap 2 . the table shows that a transmission standby duration ( time ) varies in accordance with the number of terminals to which the access point ap 2 is connected . since it is expected that the frequency of data transmission is increased as the number of connected terminals increases , the transmission standby duration is reduced . fig1 shows a transmission standby designation frame transmitted from the access point ap 2 to the terminals 2 and 3 under its control . by designating a destination mac address with a transmission standby terminal designation bit that follows the standby instruction bit in the data field df , the terminals 2 and 3 to be made to wait for transmission can be designated . in the wireless lan system having the priority data transmission function , when a new terminal that does not have data transmission priority is connected while a terminal in the wireless zone is already in a transmission standby state , the transmission standby instruction can be issued to the new terminal . fig1 shows the operation procedure at the access point ap . even if the terminal that does not have data transmission priority is newly connected in the data transmission standby state , the access point ap transmits the transmission standby instruction to the new terminal to prevent the terminal performing priority data transmission from being obstructed ( interrupted ). moreover , in the wireless lan system , as shown in fig1 , the access point ap confirms the presence of a terminal in the wireless zone under its control through regular connection between the access point ap and the terminals based on the operation procedure of monitoring the movement ( disconnection ) of the terminals . moreover , when the access point ap receives a movement notification from the wired nw after the disconnection of the terminal , the access point ap transmits the transmission standby frame to the terminal under its control based on the operation procedure shown in fig1 . in the wireless lan system having the priority data transmission function described above , as shown in fig1 , when the terminal 1 ( stal ) connected to the access point ap 1 moves to the access point ap 2 , the access point ap 1 transmits a movement ( disconnection ) notification of the terminal 1 to the access point ap 2 through the wired nw . the access point ap 2 transmits the transmission standby instruction to the terminal 2 ( sta 2 ) under its control . the terminal 2 waits for data transmission until it receives an instruction indicating transmission standby release or until transmission standby timeout . meanwhile , the terminal 1 has priority in data transmission to the access point ap 2 . although the terminal 3 ( sta 3 ) in fig1 is not illustrated in the operation sequence shown in fig1 , it operates in the same manner as that of the terminal 2 . next , a specific example of a wireless lan system in an embodiment of the present invention will be described . fig2 is a view for explaining a fundamental structure of a wireless lan system in an embodiment of the present invention . fig2 is a view showing a fundamental structure of the access points ap 1 and ap 2 and the terminals 1 and 2 in the wireless lan system shown in fig2 . an environment of the wireless lan system having the priority data transmission function shown in fig2 is fundamentally the same as that of the wireless lan system shown in fig1 . specifically , in the wireless lan system , the plurality of access points ap 1 and ap 2 are logically connected in cascade arrangement to the wired network ( the wired nw ) constituted by the wired lan . the wireless channel ch 6 is used in the wireless zone rz 1 under the control of the access point ap 1 , whereas the wireless channel ch 1 is used in the wireless zone rz 2 under the control of the access point ap 2 . each of the access points ap 1 and ap 2 and the terminals 1 and 2 operates at a wireless frequency signal assigned to it . herein , the terminal 1 present in the wireless zone rz 1 under the control of the access point ap 1 moves from the wireless zone rz 1 into the wireless zone rz 2 under the control of the access point ap 2 . in the wireless zone rz 2 under the control of the access point ap 2 , the terminal 2 is already present to perform data communication with the access point ap 2 . referring to fig2 , each of the access points ( the communication control devices ) ap 1 and ap 2 includes , as a fundamental structure , a wireless lan section 11 , a connection management section 12 , a movement notification section 13 and a transmission standby management section 14 . each of the wireless lan sections 11 performs communication ( wireless lan communication ) in a wireless area ( a wireless lan area ) with a corresponding terminal through a predetermined wireless channel . each of the connection management sections 12 confirms a connection query request and a response with the corresponding terminal . each of the movement notification sections 13 generates a terminal movement ( advance ) notification and transmits it to the other access point ap connected to the wired nw if the terminal that desires to transmit data by priority cannot be registered or the connection with the registered terminal cannot be confirmed . when receiving the terminal movement notification from the wired nw , each of the transmission standby management sections 14 generates a transmission standby instruction and transmits it to the terminal under its control through the wireless lan section 11 . each of the terminals 1 and 2 includes a wireless lan section 21 , a frame analysis section 22 , a query processing section 23 and a data transmission management section 24 . each of the wireless lan sections 21 performs wireless lan communication with a corresponding access point . each of the frame analysis sections 22 analyzes a frame from the corresponding access point to perform a sorting processing of the received frame . each of the query processing sections 23 generates a response frame to the connection query from the corresponding access point and transmits it to the wireless lan section 21 . each of the data transmission management sections 24 manages the start and the stop of data transmission . at the same time , when receiving a transmission stop instruction from the frame analysis section 22 , the data transmission management section stops the data transmission . referring collectively to fig2 and 21 , in the wireless lan system , the query for confirming the connection from the access point ap 1 and the response to it ( a procedure 9 - 1 ) are implemented through the wireless lan sections 11 and 21 between the access point ap 1 connected to the wired nw , and the terminal 1 under its control . the data transmission management section 24 of the terminal 1 transmits data ( a procedure 9 - 2 ) to the access point ap 1 through the wireless area . a mac address of the terminal 1 that desires to transmit data by priority is preregistered in the movement notification section 13 of the access point ap 1 . when the terminal 1 does not respond to a query from the access point ap 1 ( in other words , the terminal 1 moves out of the wireless zone rz 1 of the access point ap 1 ), the movement notification section 13 transmits a terminal movement notification ( a procedure 9 - 3 ) to the other access point ap 2 connected to the wireless nw . the transmission standby management section 14 of the access point ap 2 receiving the terminal movement notification transmits a transmission standby instruction ( a procedure 9 - 4 ) to the terminal 2 under its control through the wireless lan section 11 . the frame analysis section 22 of the terminal 2 receiving the transmission standby instruction through the wireless lan section 21 instructs the data transmission management section 24 to stop the data transmission to the access point ap 2 ( a procedure 9 - 5 ). when the terminal 1 moves to the access point ap 2 in this state , the terminal 1 can transmit data by priority to the access point ap 2 because the terminal 2 having transmitted data to the access point ap 2 is no longer present ( in other words , in a data transmission standby state ). as shown in fig2 , between the access point ap 1 connected to the wired nw and the terminal 1 in the wireless zone rz 1 under the control of the access point ap 1 , the query for confirming the connection from the access point ap 1 and the response to it ( a procedure 10 - 1 ) are implemented through the wireless lan sections 11 and 21 . the data transmission management section 24 of the terminal 1 transmits data ( a procedure 10 - 2 ) to the access point ap 1 through the wireless area . a mac address of the terminal 1 is preregistered as a terminal that desires to transmit data by priority in the movement notification section 13 of the access point ap 1 . when the terminal 1 does not respond to the query from the access point ap 1 , that is , it is determined that the terminal 1 exits from the wireless zone rz 1 of the access point ap 1 , the movement notification section 13 transmits a terminal movement notification ( a procedure 10 - 3 ) to the other access point ap 2 connected to the wired nw by using the terminal movement notification frame shown in fig1 . the transmission standby management section 14 of the access point ap 2 receiving the terminal movement notification transmits a transmission standby instruction ( a procedure 10 - 4 ) to the terminal 2 under its control through the wireless lan section 11 . in the terminal 2 , the frame analysis section 22 receiving the transmission standby instruction through the wireless lan section 21 instructs the data transmission management section 24 to stop the data transmission ( a procedure 10 - 5 ) to stop the data transmission to the access point ap 2 . the terminal 1 moves from the wireless zone rz 1 to the wireless zone rz 2 to be connected to the access point ap 2 . since there is no terminal transmitting data to the access point ap 2 at this time , the data transmission to the access point ap 2 is possible . in the terminal 1 , when the data transmission to the access point ap 2 is completed , the data transmission management section 24 notifies the access point ap 2 of the completion of transmission ( a procedure 10 - 7 ) through the wireless lan section 21 . at the access point ap 2 , the transmission standby management section 14 receiving the transmission completion notification through the wireless lan section 11 transmits a transmission start instruction ( a procedure 10 - 8 ) to the terminal 2 in the transmission standby state under its control through the wireless lan section 11 . the frame analysis section 22 of the terminal 2 receiving the transmission start instruction through the wireless lan section 21 instructs the data transmission management section 24 to start the transmission ( a procedure 10 - 9 ) to allow the data transmission to be restarted . fig2 is an explanatory view of the operation of the transmission standby management section 14 provided in the access point ap 2 in the wireless lan system shown in fig2 . when the received frame is a terminal movement notification frame from the wired nw , the transmission standby management section 14 generates a transmission standby instruction frame to transmit the transmission standby instruction frame to the terminal 2 under its control ( procedures 2 - 1 and 2 - 2 ). when the transmission standby management section receives the notification of completion of the transmission from the terminal 1 currently transmitting data by priority , which is already in the transmission standby state , a transmission start instruction frame is generated to be transmitted to the terminal 2 in the transmission standby state ( a procedure 2 - 3 ). fig2 is an operation sequence diagram in the wireless lan system shown in fig2 . as shown in fig2 , when the terminal 1 connected to the access point ap 1 moves to the access point ap 2 , the access point ap 1 transmits a notification of movement ( disconnection ) of the terminal 1 to the access point ap 2 through the wired nw . the access point ap 2 transmits a transmission standby instruction to the terminal 2 under its control . the terminal 2 waits for data transmission until it receives the transmission start instruction . meanwhile , the terminal 1 can transmit data by priority to the access point ap 2 . the terminal 1 that completes the data transmission notifies the access point ap 2 of the completion of transmission . the access point ap 2 receiving the completion of transmission transmits a transmission start instruction to the terminal 2 in the data transmission standby state under its control . in response to the transmission start instruction , the terminal 2 restarts the data transmission . fig2 is an example of application of the wireless lan system shown in fig2 . as illustrated , in the example of application , a patroller using the terminal 1 transmits a video image at each monitor point to a control post ( a monitor center ) connected to the wired nw while moving in the wireless zones under the control of the access points ap 1 and ap 2 . since the control post performs centralized monitoring based on the video images ( patrol video images ) from the terminal 1 of the patroller , the patrol video images are desired to be received by priority when the patroller moves between the monitor points . therefore , data from the other terminal 2 at the point to which the patroller moves is made to wait for transmission . according to the example of application , the control post on the wired nw can receive video images at a disaster site showing a state of a river or the like earlier than any other data in the event of a disaster . as shown in fig2 , the access point ap 2 controlling the wireless zone rz 2 at the destination of the terminal 1 further includes a timer section 15 and a connection number management section 16 . the timer section 15 generates a timer value after the transmission of the transmission standby instruction from the transmission standby management section 14 in consideration of the case where the transmission completion ( a procedure 11 - 1 ) from the terminal 1 that has completed the priority data transmission in the first operation example described above is not received by the access point ap 2 due to an error in the wireless area . even if the transmission standby management section 14 of the access point ap 2 does not receive the transmission completion notification transmitted from the data transmission management section 24 of the terminal 1 , the transmission start instruction ( a procedure 11 - 2 ) is transmitted in response to timeout of the timer value to transit the terminal 2 from the data transmission standby state to the data transmission restart state . furthermore , the connection number management section 16 has a function of changing the timer value in accordance with the number of terminals connected to the access point ap 2 to regulate a data transmission standby duration of the terminal 2 . fig2 is an explanatory view of an operation of the connection number management section 16 provided in the access point ap 2 in the wireless lan system shown in fig2 . when the connection number management section 16 is notified of the reception of the terminal movement notification from the access point ap 1 through the wired nw , it determines a timer value in accordance with the number of currently connected terminals ( the number of connections ). the timer value determined in the connection number management section 16 is set to the timer section 15 . in this example , when the number of connections is “ 1 ”, the transmission standby timer value is 2 sec . ( seconds ). when the number of connections is “ 5 ” or more , the transmission standby timer value is 100 msec . ( milliseconds ). in this manner , the transmission standby timer value is determined to decrease as the number of connections increases . fig2 is an operation sequence diagram in the wireless lan system shown in fig2 . as shown in fig2 , at the access point ap 2 , after the timer value is determined in accordance with the number of connected terminals , the timer is started . as a result , even if the access point ap 2 cannot receive the transmission completion notification from the terminal 1 , it can allow the terminal 2 in the transmission standby state to restart the data transmission in response to the occurrence of timeout . fig2 shows an example of application of the wireless lan system shown in fig2 . as illustrated , in the example of application , the patroller using the terminal 1 transmits video images at each monitor point to the control post connected to the wired nw while moving in the wireless zones under the access points ap 1 and ap 2 . since the control post performs centralized monitoring based on the video images ( patrol video images ) from the terminal 1 of the patroller , the patrol video images are desired to be received by priority when the patroller moves between the monitor points . therefore , data from the other terminal 2 at the point to which the patroller moves is made to wait for transmission . according to this , the transmission completion notification from the terminal 1 used by the patroller cannot be received at the access point ap 2 in some cases because of the occurrence of an error in the wireless area . even in such a case , the data transmission of the terminal 2 in the transmission standby state can be restarted in response to timeout of the timer ( the timer section 15 ). moreover , when a large number of terminals are connected under the control of the access point ap 2 , the frequency of data transmission is expected to be increased . even in such a case , since the timer value can be decreased in accordance with the number of connected terminals , the data transmission standby period can be reduced . in an environment of the wireless lan system having the priority data transmission function shown in fig3 , the terminals 2 and 3 are connected under the control of the access point ap 2 . data transmitted from the terminal 3 is video data from a fixed camera installed at the monitor point . therefore , since priority cannot be given only to the data transmission from the terminal 1 moving from the access point ap 1 , only the terminal 2 is made to wait for the data transmission . at this time , the frame illustrated in fig1 is used as a transmission standby designation frame transmitted from the access point ap 2 . at the access point ap 2 , a mac address of the terminal 3 that does not wait for transmission is preset . on the other hand , the access point ap 2 designates an mac address of the terminal 2 waiting for transmission based on the preset mac address to bring it into a transmission standby state . as a result , since it is possible to designate the terminal 2 that is desired to be made to wait for transmission , the order of priorities of data transmission in the wireless zone rz 2 can be determined . as shown in fig3 , the access point ap 2 controlling the wireless zone rz 2 at the destination of the terminal 1 further includes a priority management section 18 having a no transmission standby setting table 17 . in the table 17 of the priority management section 18 , a mac address of a terminal ( the terminal 3 ) that does not wait for transmission is preregistered . the transmission standby management section 14 searches for a terminal that does not wait for transmission in the table 17 in the priority management section 18 . since the mac address of the terminal 3 , 00 : 51 : 36 : 22 : 96 : 31 , is set as identification information in the setting table 17 , the mac address is removed from the list of terminals currently connected to the access point ap 2 . then , the transmission standby designation frame is generated to be transmitted . as a result , the data transmission right is passed between the terminal 3 that does not wait for transmission and the terminal 1 that desires to transmit data by priority . fig3 is an operation sequence diagram in the wireless lan system shown in fig3 and 31 . as shown in fig3 , since the terminal 3 is not in the transmission standby state , interrupt data transmission is possible during the data transmission of the terminal 1 . since the terminal 1 does not have absolute priority , the data transmission efficiency is lowered as compared with the case where it has the absolute priority . however , the access point ap 2 can receive the data from both the terminals 1 and 3 . fig3 shows an access procedure of the terminals 1 , 2 and 3 in the wireless lan system shown in fig3 and 31 . as shown in fig3 , only the terminal 2 is brought into a transmission standby state in response to the transmission standby instruction from the access point ap 2 . the terminals 1 and 3 cannot transmit data during their data transmission because it is determined that the wireless area is busy . however , it is determined that the wireless area is free based on transmission intervals after the data transmission to enable the data transmission . in an environment of the wireless lan system having the priority data transmission function shown in fig3 , the terminal 2 present in the wireless zone rz 2 under the control of the access point ap 2 is already in a transmission standby state . when the terminal 3 in the wireless zone rz 2 is newly connected to the access point ap 2 in this state , the terminal 3 can transmit data because the transmission standby instruction is not issued to it . even if the terminal 1 moves from the wireless zone rz 1 under the control of the access point ap 1 to the wireless zone rz 2 under the control of the access point ap 2 , it cannot transmit data by priority . as shown in fig3 , the access point ap 2 controlling the wireless zone rz 2 at the destination of the terminal 1 further includes a connection management section 19 . at the access point ap 2 receiving a wireless link frame of a wireless connection request ( a procedure 13 - 1 ) from the new terminal 3 , the connection management section 19 recognizes the connection of the new terminal 3 to notify the transmission standby management section 14 of the new terminal ( a procedure 13 - 2 ). the transmission standby management section 14 receiving the notification transmits the transmission standby instruction to the terminal 3 ( a procedure 13 - 3 ). as a result , even if the new terminal 3 , which is already in the transmission standby state , is connected in the wireless zone rz 2 , the data transfer efficiency of the terminal 1 that desires to transmit data by priority can be prevented from being degraded ( obstructed ) because the transmission standby instruction can be issued to the terminal 3 . the processes in the embodiment described above are provided as a program executable on a computer , and can be provided through a recording medium such as a cd - rom or a flexible disk or furthermore through a communication line . a plurality of arbitrary ones of or all of the processes in the embodiment described above can be selected to be executed in combination .