JP4407214B2 - Wireless LAN system - Google Patents

Description

  The present invention relates to a wireless LAN system including a wireless access point and a wireless LAN terminal, and more particularly to a wireless LAN system that performs roaming at high speed when the wireless LAN terminal moves.

  In recent years, a wireless LAN (Local Area Network) system represented by IEEE (Institut of Electrical and Electronics Engineers) 802.11 has been widely used. The wireless LAN system includes a wireless LAN terminal and a wireless access point capable of transmitting / receiving information to / from the wireless LAN terminal via a wireless communication line.

  The use method of the wireless LAN system is not only used as a LAN but also as a use method as an infrastructure of a mobile phone system using VoIP (Voice over Internet Protocol).

  When a wireless LAN system is used as an infrastructure of a mobile phone system, a wireless LAN terminal can wirelessly communicate with a single wireless access point when a user of the wireless LAN terminal (mobile phone) moves during a call. The user may have moved from a position to a position where wireless communication with another wireless access point is possible. Roaming means that a wireless LAN terminal moves while continuing communication, disconnects (assigns) from one wireless access point, and connects (attaches) to another wireless access point. Here, the fact that a wireless LAN terminal transmits / receives information to / from a specific wireless access point is said to belong to that wireless access point.

  For convenience, it is desirable to maintain a call even during roaming. Further, while roaming, the call is interrupted for searching for a wireless access point, etc., but it is desirable that the time for which the call is interrupted is as short as possible.

  FIG. 9 is a sequence diagram showing an example of operation during roaming in a conventional wireless LAN system. Here, an example will be described in which a conventional wireless LAN system is a system compliant with IEEE 802.11.

  The wireless LAN terminal transmits a probe request (hereinafter referred to as a probe request) to the wireless access point, and the wireless access point that has received the probe response (hereinafter referred to as a probe response) sends a probe response to the wireless LAN terminal. Transmit (steps S301 and S302). When receiving the probe response, the wireless LAN terminal knows that there is a wireless access point to which it can belong. The wireless LAN terminal that has received the probe response transmits an Authentication Request (hereinafter referred to as an authentication request) to the wireless access point, and the wireless access point that has received the authentication request is referred to as an Authentication Response (hereinafter referred to as an authentication response). Is transmitted to the wireless LAN terminal to perform authentication processing for connection to the wireless access point (steps S303 and S304). The wireless LAN terminal that has received the authentication response transmits an association request (hereinafter referred to as an association request) to the wireless access point to request the wireless access point to the wireless access point, and the wireless access point that has received the association request Then, an association response (hereinafter referred to as an association response) is transmitted to the wireless LAN terminal to allow the wireless LAN to belong to the wireless access point (steps S305 and S306). Then, the wireless LAN terminal can belong to the wireless access point.

  When the electric field strength of the signal received from the wireless access point decreases, the wireless LAN terminal scans the wireless access point by sequentially transmitting a probe request to each wireless channel defined by IEEE 802.11 (step S307). To S310). The wireless access point that has received the probe request transmits a probe response to the wireless LAN terminal (step S311). When receiving the probe response, the wireless LAN terminal knows that there is a wireless access point to which it can belong. The wireless LAN terminal that has received the probe response transmits an authentication request to the wireless access point, and the wireless access point that has received the authentication request transmits an authentication response to the wireless LAN terminal to perform authentication processing of belonging to the wireless access point. This is performed (steps S312 and S313).

  The wireless LAN terminal that has received the authentication response transmits an association request to the wireless access point to request wireless LAN belonging to the wireless access point, and the wireless access point that has received the association request transmits an association response to the wireless LAN terminal. Then, the wireless LAN is allowed to belong to the wireless access point (steps S314 and S315).

  As described above, when a conventional wireless LAN system detects a decrease in electric field strength of a signal received from a wireless access point, it scans the wireless access point and attempts to belong to the wireless access point that transmitted the probe response. During this time, if the electric field strength significantly decreases, communication between the wireless LAN terminal and the wireless access point is interrupted.

  When a wireless LAN terminal transmits a probe request in order to each wireless channel specified by IEEE 802.11, it immediately tries to belong to a wireless access point that is geographically adjacent to the wireless access point to which the wireless LAN terminal currently belongs. Not necessarily. In the example of FIG. 9, as a result of scanning the wireless access point, it can belong to the wireless access point that transmitted the fourth probe request. In such a case, the communication (call) interruption time becomes long.

As a method of performing roaming at high speed, there are a method described in Patent Document 1 and a method described in Patent Document 2. The method described in Patent Document 1 and the method described in Patent Document 2 are applied to a wireless LAN system using frequency hopping, and by obtaining frequency hopping information of a roaming destination wireless access point, the roaming destination The frequency for communicating with the wireless access point is specified to realize high-speed roaming.
Japanese Unexamined Patent Publication No. 2001-94572 (page 4-7, FIG. 1) JP 2002-26931 A (page 4-9, FIG. 1)

  However, the methods described in Patent Literature 1 and Patent Literature 2 have a problem in that it is necessary to perform synchronization for frequency hopping, and control of the wireless access point side network becomes complicated. The methods described in Patent Document 1 and Patent Document 2 are intended for a wireless LAN system using frequency hopping, and are applied to a wireless LAN system using a direct sequence (direct spreading) method (DS method). I can't.

  Therefore, an object of the present invention is to provide a wireless LAN system that realizes high-speed roaming without imposing a load on the control of a wireless access point side network in a wireless LAN system using a direct sequence method.

A wireless LAN system according to the present invention includes a wireless LAN terminal and a plurality of wireless access points that can transmit and receive information to and from the wireless LAN terminal via a wireless communication line and connect the communication network and the wireless LAN terminal. In the wireless LAN system, each wireless access point periodically transmits a beacon signal including information for identifying the wireless access point, is connected to the wireless access point via a communication network, and is geographically connected to the wireless access point. A roaming information setting terminal for transmitting roaming information, which is information of other adjacent wireless access points, to the wireless access point, the wireless access point storing storage means for storing the roaming information, and wireless communication with the wireless LAN terminal Roaming information by sending and receiving information over the line And a wireless LAN communication means for transmitting to the wireless LAN terminal, a wireless LAN communication means of the wireless access point may transmit roaming information to the wireless LAN terminal when the wireless LAN terminal belongs, the wireless LAN terminal, a wireless access point And terminal wireless communication means for transmitting and receiving information via a wireless communication line, terminal storage means for storing received roaming information, and terminal wireless communication means based on roaming information stored in the terminal storage means The wireless access point includes terminal control means for causing the wireless LAN terminal and the wireless access point to perform information transmission / reception via a wireless communication line, and the terminal control means includes a signal indicating that the terminal wireless communication means Is received, the information included in the beacon signal is extracted as access point attribution candidate information and the terminal憶means is stored, the wireless LAN terminal, on the basis of the access point belongs destination candidate information included in the beacon signal to the terminal wireless communication unit is received from the wireless access point, the transmission source wireless access point of the beacon Including an access point ranking means for ranking , and the terminal wireless communication means monitors the electric field strength of the signal of the wireless communication line received from the wireless access point, and indicates that when the electric field strength falls below a predetermined value. The terminal control means notifies the terminal control means, and when the terminal wireless communication means receives the beacon signal, the terminal control means of the wireless LAN terminal extracts access point attribution candidate information and stores it in the terminal storage means. When a notification is received that the value has dropped below a predetermined value, it belongs to one wireless access point based on roaming information , If the terminal control means of the wireless LAN terminal cannot be assigned to one wireless access point based on the roaming information, the terminal wireless means based on the access point attribution candidate information stored in the terminal storage means The communication means is attributed to another wireless access point .

  The terminal wireless communication means of the wireless LAN terminal, for example, monitors the electric field strength of the signal of the wireless communication line received from the wireless access point, and notifies the terminal control means when the electric field strength falls below a predetermined value. Then, when receiving the notification that the electric field strength has dropped below a predetermined value, the terminal control means searches for and belongs to another wireless access point based on the roaming information. According to such a configuration, when the wireless LAN terminal moves and the field strength of the signal of the wireless communication line received from one wireless access point decreases, it belongs to another wireless access point based on roaming information. Therefore, it is possible to roam at high speed without searching for another wireless access point, and to move the wireless LAN terminal while being connected to the communication network.

  The wireless LAN communication means of the wireless access point preferably transmits roaming information to the wireless LAN terminal when the wireless LAN terminal belongs. According to such a configuration, it is possible to transmit roaming information to the wireless LAN terminal before the wireless LAN terminal moves and the electric field strength of the signal received from the wireless access point decreases.

  The roaming information transmitted by the wireless access point includes, for example, information related to the WEP key.

  In the wireless LAN system, the wireless LAN communication means of the wireless access point transmits an indicator signal including access point attribution candidate information that is information for identifying the wireless access point at a predetermined timing, and the terminal control means of the wireless LAN terminal The terminal wireless communication means may be configured to extract access point attribution candidate information and store it in the terminal storage means when receiving the indicator signal. According to such a configuration, even when the terminal storage unit of the wireless LAN terminal does not store roaming information, the wireless access point is automatically scanned to identify a wireless access point that is a candidate for belonging. Can do.

  If the terminal control means of the wireless LAN terminal cannot be attributed to one wireless access point based on the roaming information, the terminal wireless means based on the access point attribution destination candidate information stored in the terminal storage means It is preferable that the communication means belong to another wireless access point. According to such a configuration, the terminal control unit of the wireless LAN terminal can perform wireless communication indicated by the access point attribution candidate information even when the terminal wireless communication unit cannot belong to the wireless access point indicated by the roaming information. The terminal wireless communication means can be attributed to the access point.

  According to the present invention, since the roaming information setting terminal stores the roaming information in each wireless access point via the communication network, the roaming information can be stored in each wireless access point from a remote location. The burden on the administrator can be reduced. Further, since the wireless access points do not transmit and receive information to and from each other, roaming information can be stored in the wireless access point without imposing a load on the control of the wireless access point side network. Further, when the wireless LAN terminal stores roaming information, the wireless access point is not searched, so that roaming can be performed at high speed.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a configuration diagram showing a configuration example of a wireless LAN system according to the present invention. Referring to FIG. 1, a wireless LAN system according to the present embodiment includes a wireless LAN terminal 103, an access point A101 (wireless access point) and an access point B102 that transmit and receive information to and from the wireless LAN terminal 103, and A wireless access point information setting terminal 104 (roaming information setting terminal) that transmits information of wireless access points geographically adjacent to each wireless access point connected via the wired LAN 105 is included.

  The wireless access point information setting terminal 104 is realized by, for example, a server and is connected to the access point A 101 and the access point B 102 via a wired LAN, and performs various settings of the wireless access point. Specifically, a wireless channel and an identifier (SSID (Service Set IDentifier)) of each wireless access point are set. For example, the access point A101 has a Web server function, and the administrator of the access point A101 operates the wireless access point information setting terminal 104 to access the access point A101 using a Web browser installed in the wireless access point information setting terminal 104. The wireless access point information setting screen stored in advance by the access point A 101 is displayed on the display unit of the wireless access point information setting terminal 104 and set.

  In the case of IEEE802.11b, the wireless channel is selected and set from 1 to 14ch (channel), and the SSID is set to an arbitrary character string. Each wireless access point may include a dedicated communication interface for setting wireless access point information. In addition, the wireless access point information setting terminal 104 performs setting of roaming information (neighboring access point information; hereinafter referred to as roaming information).

  FIG. 2 is a block diagram illustrating a configuration example of the access point A101. Access point B102 has the same internal configuration as access point A101 shown in FIG. Hereinafter, the access point B102 will be described with reference to the internal configuration of the access point A101.

  Referring to FIG. 2, the access point A 101 receives information from the wireless access point information setting terminal 104 via the wired LAN 105 and transmits / receives information to / from other devices connected via the wired LAN. A wired LAN communication unit 201, a wireless LAN communication unit 203 (wireless LAN communication means) which is a communication interface for transmitting and receiving information to and from the wireless LAN terminal 103, and storage of various setting values of the access point A101. And a storage unit 204 (storage unit) used as a buffer for temporarily storing communication data, a control unit 202 that is realized by a CPU and controls each unit of the access point A 101, and an antenna 208. IEEE 802.3 is a specific example of a standard for realizing a wired LAN, but the present invention is not limited to this.

  Various setting values stored in the storage unit 204 include roaming information set by the wireless channel, SSID, and wireless access point information setting terminal 104, and the wireless LAN communication unit 203 transmits the roaming information to the wireless LAN terminal 103.

  FIG. 3 is a block diagram illustrating a configuration example of the wireless LAN terminal 103. Referring to FIG. 3, the wireless LAN terminal 103 includes a terminal wireless communication unit 205 (terminal wireless communication means) that is a communication interface for transmitting / receiving information to / from the access point A 101 and the access point B 102 via the wireless LAN, and the wireless LAN terminal 103. A terminal storage unit 207 (terminal storage unit) used as a buffer for temporarily storing various setting values and a buffer for temporarily storing communication data, and a terminal control unit 206 (which is realized by a CPU and controls each unit of the wireless LAN terminal 103) Terminal control means) and an antenna 209. The terminal wireless communication unit 205 has a function of measuring the electric field strength of the received wireless signal. The terminal storage unit 207 stores an access point attribution candidate list. The wireless LAN terminal 103 is realized by a mobile phone having a wireless LAN communication function.

  The access point attribution candidate list stored in the terminal storage unit 207 of the wireless LAN terminal 103 will be described. FIG. 4 is an explanatory diagram of a configuration example of the access point attribution destination candidate list. The access point attribution candidate list specifies whether “Channel” indicating the wireless channel, “SSID” indicating the SSID of the wireless access point, and WEP (Wired Equivalent Privacy) for encrypting transmission / reception data are applied. This includes a “WEP ON / OFF” and a “WEP key” indicating a WEP key.

  The access point attribution candidate list is configured by information of one or a plurality of wireless access points, set by the user of the wireless LAN terminal 103, or searched by the wireless LAN terminal 103 to automatically access the access point attribution destination. It is generated by adding wireless access point information to the candidate list. Further, for example, the wireless access points are ranked according to user settings, the date and time added to the access point attribution candidate list, and the like.

  A method will be described in which the wireless LAN terminal 103 searches the surroundings and automatically adds wireless access point information to the access point attribution destination candidate list. The wireless LAN communication unit 203 of the access point A101 periodically outputs a beacon using a predetermined wireless channel. The beacon output by the wireless LAN communication unit 203 includes “SSID”, “WEP ON / OFF”, and “WEP key” information (access point attribution destination candidate information). Then, the terminal control unit 206 of the wireless LAN terminal 103 controls the terminal wireless communication unit 205 to continuously receive each wireless channel (1ch to 14ch in the example of IEEE802.11b). Identify the radio channel. Then, by associating the specified beacon with the information on the wireless channel that has received the beacon, it is possible to acquire information constituting the access point attribution destination candidate list shown in FIG.

  The roaming information that each wireless access point transmits to the wireless LAN terminal 103 will be described. FIG. 5 is an explanatory diagram showing a configuration of roaming information. The roaming information is wirelessly transmitted from the wireless access point in an association procedure (hereinafter referred to as an association procedure) performed between the wireless LAN terminal 103 and the wireless access point when the wireless LAN terminal 103 belongs to the wireless access point. It is included in the association response transmitted to the LAN terminal 103 and transmitted to the wireless LAN terminal 103. For example, as shown in FIG. 4, it is added to each element defined in IEEE 802.11. The association procedure will be described later.

  “Elemant ID” is an identifier indicating that the element is roaming information. “Length” indicates the data length (number of bytes) of the element. In addition, since each element from “Channel” to “WEP key” is the same as the element included in the access point attribution candidate list, description thereof is omitted.

  A case where WEP is applied to transmission / reception of information between each wireless access point and the wireless LAN terminal 103 will be described. Each wireless access point performs encryption of information transmitted to the wireless LAN terminal 103 and decryption of information received from the wireless LAN terminal 103 using a WEP key. The wireless LAN terminal 103 performs encryption of information transmitted to each wireless access point and decryption of information received from each wireless access point based on the WEP key included in the received roaming information.

  Next, the operation of the wireless LAN system of the present invention will be described. FIG. 6 is a flowchart showing the operation of the wireless LAN system of the present invention. The terminal wireless communication unit 205 of the wireless LAN terminal 103 always measures and monitors the electric field strength of the signal received from the wireless access point to which the wireless LAN terminal 103 belongs (step S101). Notify the control unit 206. When receiving a notification that the electric field strength is equal to or less than a predetermined threshold, the terminal control unit 206 starts searching for a wireless access point that is geographically adjacent to the wireless access point to which the terminal control unit 206 belongs. Here, the predetermined threshold value of the electric field strength is set near the lower limit of the electric field strength capable of communicating with the wireless access point, and is stored in advance in the terminal storage unit 207 of the wireless LAN terminal 103.

  A search for a wireless access point geographically adjacent to the wireless access point to which the terminal control unit 206 belongs will be described. First, it is determined whether roaming information has already been received from the belonging wireless access point (step S102). The terminal control unit 206 searches the content stored in the terminal storage unit 207 and determines whether roaming information has already been received. If the terminal control unit 206 determines that the roaming information has already been received, the wireless access point indicated by the roaming information is a wireless access point that is geographically adjacent to the currently belonging wireless access point, Judge as a candidate. Then, based on the “Channel” and “SSID” of the roaming information, a probe request is transmitted to the wireless access point indicated by the roaming information that is the candidate for the attribution destination (step S103).

  When a probe response to the probe request is received from the wireless access point, it tries to belong to the wireless access point (step S104). If you can be attributed, you have successfully roamed.

  Even if the roaming information has been received, if the terminal control unit 206 determines that it has not been able to belong to the wireless access point to which it has attempted to attach or if the roaming information has not been received, the terminal Based on the access point attribution destination candidate list stored in the storage unit 207, a probe request is sequentially transmitted to each wireless access point to attempt attribution (step S105). If the terminal wireless communication unit 205 of the wireless LAN terminal 103 receives the probe response and can be attributed, it means that roaming has succeeded (step S106).

  Even if probe requests are sequentially transmitted to the wireless access points described in the access point attribution destination candidate list, roaming has failed if no assignment can be made to any wireless access point. If the roaming fails, the terminal control unit 206 scans another wireless access point using a conventional wireless LAN system method. That is, the wireless LAN terminal sequentially transmits a probe request to each wireless channel specified by IEEE 802.11. And it tries to belong to the wireless access point which transmitted the probe response.

  If roaming fails, the terminal control unit 206 may continue communication with the currently belonging wireless access point. However, in this state, detection of a decrease in electric field strength and search for a wireless access point are repeated, and communication (call) is interrupted for a long time. Therefore, if the attribution is impossible in the determination of the attribution possibility based on the access point attribution destination candidate list (step S105), the wireless access point may not be searched for a certain period of time.

  Next, transmission / reception of information between the wireless LAN terminal 103 and the access point A 101 and access point B 102 will be described by taking the IEEE 802.11 standard as an example. FIG. 7 is a sequence diagram illustrating transmission / reception of information between the wireless LAN terminal 103 and the access point A 101 and access point B 102.

  The wireless LAN terminal 103 transmits a probe request to the access point A101, and the access point A101 that has received the probe request transmits a probe response to the wireless LAN terminal 103 (steps S201 and S202). When receiving the probe response, the wireless LAN terminal 103 knows that there is a wireless access point to which it can belong. When the wireless LAN terminal 103 receives the probe response, the wireless LAN terminal 103 transmits an authentication request to the access point A 101, and the access point A 101 that has received the authentication request transmits an authentication response to the wireless LAN terminal 103 to authenticate the belonging to the access point A 101. Processing is performed (steps S203 and S204).

  The wireless LAN terminal 103 that has received the authentication response transmits an association request to the access point A 101 to request the wireless LAN belonging to the access point A 101, and the access point A 101 that has received the association request associates with the wireless LAN terminal 103. A response is transmitted, and an association procedure, which is a procedure for permitting wireless LAN belonging to the access point A101, is performed (steps S205 and S206). Then, the wireless LAN terminal 103 can belong to a wireless access point. Here, the association response includes roaming information that is information regarding the access point B102. The terminal storage unit 207 of the wireless LAN terminal 103 stores roaming information.

  When the terminal control unit 206 of the wireless LAN terminal 103 detects that the electric field strength of the signal transmitted / received to / from the access point A 101 is reduced, the probe request is made based on the roaming information stored in the terminal storage unit 207. Is transmitted to the access point B102 (step S207). When receiving the probe request, the access point B 102 transmits a probe response to the wireless LAN terminal 103 (step S208). Upon receiving the probe response, the wireless LAN terminal 103 transmits an authentication request to the access point B102, and the access point B102 that has received the authentication request transmits an authentication response to the wireless LAN terminal 103 to authenticate the belonging to the access point B102. Processing is performed (steps S209 and S210).

  The wireless LAN terminal 103 that has received the authentication response transmits an association request to the access point B 102 to request a wireless LAN connection to the access point B 102, and the access point B 102 that has received the association request associates with the wireless LAN terminal 103. A response is transmitted to allow wireless LAN connection to access point B102 (steps S211 and S212).

  So far, as shown in the example of FIG. 5, the association response has been described as including one piece of roaming information, but the association response may include a plurality of roaming information. The structure of the association response in such a case is shown in FIG. When such a configuration is applied to a wireless access point having a plurality of adjacent wireless access points, the wireless LAN terminal 103 selects one of the plurality of roaming information and sets the wireless access point indicated by the selected roaming information. A probe request can be sent. Further, even if connection to one wireless access point fails, a probe request can be transmitted to another wireless access point based on other roaming information.

  As described above, IEEE 802.11 has been described as an example of a wireless LAN, but the present invention is not limited to this.

  According to this embodiment, when the wireless LAN terminal 103 stores roaming information, the wireless access point is not searched even when the electric field strength of the received signal is reduced, so that roaming is performed at high speed. be able to.

  When the wireless LAN terminal 103 moves and the electric field strength of the signal received from the wireless access point to which the wireless LAN terminal 103 belongs is lowered, roaming can be performed at high speed to wireless access points that are geographically adjacent.

It is a block diagram which shows the example of 1 structure of the wireless LAN system by this invention. It is a block diagram which shows one structural example of the wireless access point by this invention. It is a block diagram which shows one structural example of the wireless LAN terminal by this invention. It is explanatory drawing which shows the example of 1 structure of the access point attribution destination candidate list | wrist by this invention. It is explanatory drawing which shows the structure of the roaming information by this invention. 3 is a flowchart showing the operation of the wireless LAN system of the present invention. It is a sequence diagram which shows operation | movement of the wireless LAN system of this invention. It is explanatory drawing which shows the other structural example of the roaming information by this invention. It is a sequence diagram which shows an example of the operation | movement at the time of roaming in the conventional wireless LAN system.

Explanation of symbols

101 Access point A
102 Access point B
103 Wireless LAN terminal 104 Adjacent access point information setting terminal 105 Wired LAN
201 wired LAN communication unit 202 control unit 203 wireless LAN communication unit 204 storage unit 205 terminal wireless communication unit 206 terminal control unit 207 terminal storage unit 208, 209 antenna

Claims (2)

A wireless LAN system including a wireless LAN terminal and a plurality of wireless access points capable of transmitting and receiving information to and from the wireless LAN terminal via a wireless communication line and connecting a communication network and the wireless LAN terminal. ,
Each wireless access point periodically transmits a beacon signal containing information identifying the wireless access point,
A roaming information setting terminal which is connected to the wireless access point via a communication network and transmits roaming information which is information of another wireless access point geographically adjacent to the wireless access point to the wireless access point;
The wireless access point is
Storage means for storing the roaming information;
Wireless LAN communication means for transmitting and receiving information to and from the wireless LAN terminal by transmitting and receiving information to and from the wireless LAN terminal via a wireless communication line;
The wireless LAN communication means of the wireless access point transmits roaming information to the wireless LAN terminal when the wireless LAN terminal belongs,
The wireless LAN terminal is
Terminal wireless communication means for transmitting and receiving information to and from the wireless access point via a wireless communication line;
Terminal storage means for storing the received roaming information;
Based on the roaming information stored in the terminal storage means, the terminal wireless communication means is transmitted to another wireless access point, and the wireless LAN terminal and the wireless access point transmit and receive information via a wireless communication line. and a terminal controller for the assignment it is carried out,
When the terminal wireless communication means receives the beacon signal, the terminal control means extracts information included in the beacon signal as access point attribution candidate information and stores it in the terminal storage means,
The wireless LAN terminal ranks the wireless access point that is the transmission source of the beacon signal based on the access point attribution candidate information included in the beacon signal that the terminal wireless communication means receives from the wireless access point includes an access point ranking unit,
The terminal wireless communication means monitors the electric field strength of the signal of the wireless communication line received from the wireless access point, and notifies the terminal control means to that effect when the electric field strength falls below a predetermined value,
When the terminal control means receives a notification that the electric field strength has dropped below a predetermined value, it belongs to one wireless access point based on the roaming information ,
If the terminal control means of the wireless LAN terminal cannot be attributed to one wireless access point based on roaming information, the terminal control means determines the terminal based on the access point attribution candidate information stored in the terminal storage means. A wireless LAN system, wherein a wireless communication means is assigned to another wireless access point . Roaming information claim 1 Symbol placement of the wireless LAN system includes information regarding WEP key wireless access point transmits.

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